Dynamin Is Functionally Coupled to Insulin Granule Exocytosis

The insulin granule integral membrane protein marker phogrin-green fluorescent protein was co-localized with insulin in Min6B1 β-cell secretory granules but did not undergo plasma membrane translocation following glucose stimulation. Surprisingly, although expression of a dominant-interfering dynamin mutant (Dyn/K44A) inhibited transferrin receptor endocytosis, it had no effect on phogringreen fluorescent protein localization in the basal or secretagogue-stimulated state. By contrast, co-expression of Dyn/K44A with human growth hormone as an insulin secretory marker resulted in a marked inhibition of human growth hormone release by glucose, KCl, and a combination of multiple secretagogues. Moreover, serial pulse depolarization stimulated an increase in cell surface capacitance that was also blocked in cells expressing Dyn/K44A. Similarly, small interference RNA-mediated knockdown of dynamin resulted in marked inhibition of glucose-stimulated insulin secretion. Together, these data suggest the presence of a selective kiss and run mechanism of insulin release. Moreover, these data indicate a coupling between endocytosis and exocytosis in the regulation of β-cell insulin secretion. The insulin granule integral membrane protein marker phogrin-green fluorescent protein was co-localized with insulin in Min6B1 β-cell secretory granules but did not undergo plasma membrane translocation following glucose stimulation. Surprisingly, although expression of a dominant-interfering dynamin mutant (Dyn/K44A) inhibited transferrin receptor endocytosis, it had no effect on phogringreen fluorescent protein localization in the basal or secretagogue-stimulated state. By contrast, co-expression of Dyn/K44A with human growth hormone as an insulin secretory marker resulted in a marked inhibition of human growth hormone release by glucose, KCl, and a combination of multiple secretagogues. Moreover, serial pulse depolarization stimulated an increase in cell surface capacitance that was also blocked in cells expressing Dyn/K44A. Similarly, small interference RNA-mediated knockdown of dynamin resulted in marked inhibition of glucose-stimulated insulin secretion. Together, these data suggest the presence of a selective kiss and run mechanism of insulin release. Moreover, these data indicate a coupling between endocytosis and exocytosis in the regulation of β-cell insulin secretion. In the basal state pancreatic β-cells secrete insulin at a low rate and following a meal increase insulin release into the circulation sufficient to maintain normal glucose homeostasis. Insulin is stored in β-cells as zinc hexamer crystals within mature granules that undergo tightly regulated exocytosis in response to extrinsic stimuli (such as glucose) that induce a cascade of events leading to the elevation of cytosolic calcium levels and/or of various second messengers (1Berggren P.O. Larsson O. Biochem. Soc. Trans. 1994; 22: 12-18Crossref PubMed Scopus (80) Google Scholar, 2Mears D. J. Membr. Biol. 2004; 200: 57-66Crossref PubMed Scopus (111) Google Scholar, 3Barg S. Pharmacol. Toxicol. 2003; 92: 3-13Crossref PubMed Scopus (60) Google Scholar). In turn, calcium functions to promote the fusion of pre-docked readily releasable granules similar to that of the calcium-regulated release of various other hormones and neurotransmitters in multiple neuroendocrine cell types (3Barg S. Pharmacol. Toxicol. 2003; 92: 3-13Crossref PubMed Scopus (60) Google Scholar). In pancreatic β-cells, it is generally accepted that there are two populations of insulin secretory granules, the readily releasable pool that is responsible for the initial (first phase) insulin secretion and a second reserve pool that is responsible for a more prolonged (second phase) insulin secretion (4Barg S. Eliasson L. Renstrom E. Rorsman P. Diabetes. 2002; 51: S74-S82Crossref PubMed Google Scholar, 5Rorsman P. Eliasson L. Renstrom E. Gromada J. Barg S. Gopel S. News Physiol. Sci. 2000; 15: 72-77PubMed Google Scholar). The readily releasable granule pool is apparently predocked at the cell surface with the Q-SNARE proteins, syntaxin 1 and SNAP25, in a complex with the granule R-SNARE protein VAMP2 and the calcium-regulated protein, synaptotagmin, although the specific synaptotagmin isoform remains unresolved (6Ohara-Imaizumi M. Nishiwaki C. Nakamichi Y. Kikuta T. Nagai S. Nagamatsu S. Diabetologia. 2004; 47: 2200-2207Crossref PubMed Scopus (50) Google Scholar, 7Nevins A.K. Thurmond D.C. J. Biol. Chem. 2005; 280: 1944-1952Abstract Full Text Full Text PDF PubMed Scopus (87) Google Scholar, 8Mizuta M. Kurose T. Miki T. Shoji-Kasai Y. Takahashi M. Seino S. Matsukura S. Diabetes. 1997; 46: 2002-2006Crossref PubMed Google Scholar, 9Brown H. Meister B. Deeney J. Corkey B.E. Yang S.N. Larsson O. Rhodes C.J. Seino S. Berggren P.O. Fried G. Diabetes. 2000; 49: 383-391Crossref PubMed Scopus (45) Google Scholar). More recently, other studies have also indicated the involvement of the syntaxin 4 isoform in insulin secretion (10Saito T. Okada S. Yamada E. Ohshima K. Shimizu K. Shimomura K. Sato M. Pessin J.E. Mori M. J. Biol. Chem. 2003; 278: 36718-36725Abstract Full Text Full Text PDF PubMed Scopus (33) Google Scholar, 11Spurlin B.A. Thurmond D.C. Mol. Endocrinol. 2006; 20: 183-193Crossref PubMed Scopus (74) Google Scholar). In any case, following the initial rapid first phase of insulin secretion, second phase secretion results from the recruitment of reserve granules to the plasma membrane that are also dependent on Q- and R-SNARE interaction for fusion. Various models describing the mechanism of insulin granule fusion with the plasma membrane have been proposed. Initial studies have suggested that the release of the insulin-containing dense core granule content occurs en masse, consistent with the formation of a plasma membrane pore that fully expands to encompass the granule membrane proteins and lipids (12Orci L. Amherdt M. Malaisse-Lagae F. Rouiller C. Renold A.E. Science. 1973; 179: 82-84Crossref PubMed Scopus (60) Google Scholar, 13Takahashi N. Kishimoto T. Nemoto T. Kadowaki T. Kasai H. Science. 2002; 297: 1349-1352Crossref PubMed Scopus (228) Google Scholar, 14Ma L. Bindokas V.P. Kuznetsov A. Rhodes C. Hays L. Edwardson J.M. Ueda K. Steiner D.F. Philipson L.H. Proc. Natl. Acad. Sci. U. S. A. 2004; 101: 9266-9271Crossref PubMed Scopus (83) Google Scholar). Alternatively, it has also been suggested that insulin granules may actually stack and communicate with each other with a given granule releasing its content into another granule leading to a continuously gating channel to the plasma membrane through a process called compound exocytosis (15Leung Y.M. Sheu L. Kwan E. Wang G. Tsushima R. Gaisano H. Biochem. Biophys. Res. Commun. 2002; 292: 980-986Crossref PubMed Scopus (33) Google Scholar, 16Kwan E.P. Gaisano H.Y. Diabetes. 2005; 54: 2734-2743Crossref PubMed Scopus (66) Google Scholar). Another model has recently been proposed in that each granule separately forms a transient plasma membrane pore with the plasma membrane resulting in the release of intraluminal cargo, and either complete mixing of the membrane components (kiss and run) or selective membrane mixing (cavicapture) followed by endocytosis and recycling of the vesicle/granule membrane proteins and lipids (17Tsuboi T. McMahon H.T. Rutter G.A. J. Biol. Chem. 2004; 279: 47115-47124Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar, 18Tsuboi T. Zhao C. Terakawa S. Rutter G.A. Curr. Biol. 2000; 10: 1307-1310Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar, 19Taraska J.W. Perrais D. Ohara-Imaizumi M. Nagamatsu S. Almers W. Proc. Natl. Acad. Sci. U. S. A. 2003; 100: 2070-2075Crossref PubMed Scopus (303) Google Scholar). Although these studies examined the trafficking/release of single granule events, we have examined the macroscopic function of dynamin in the regulation of insulin secretion. Consistent with previous studies (18Tsuboi T. Zhao C. Terakawa S. Rutter G.A. Curr. Biol. 2000; 10: 1307-1310Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar), inhibition of endocytosis does not lead to the appearance of the insulin granule membrane marker phogrin at the cell surface suggesting the transient opening of a selective granule-plasma membrane pore. Surprisingly however, expression of a dominant-interfering dynamin mutant or siRNA 3The abbreviations used are: siRNA, small interference RNA; hGH, human growth hormone; Dyn, dynamin; EGFP, enhanced green fluorescent protein; WT, wild type. -mediated dynamin knockdown resulted in a marked inhibition of insulin secretion. These data indicate the presence of a direct coupling between insulin granule exocytosis (fusion pore opening) and endocytosis (fusion pore closure) events. Cell Culture and Transfection—Min6B1 (transformed mouse β) cells (20Lilla V. Webb G. Rickenbach K. Maturana A. Steiner D.F. Halban P.A. Irminger J.C. Endocrinology. 2003; 144: 1368-1379Crossref PubMed Scopus (116) Google Scholar) were grown at 37 °C in 5% CO2 in Dulbeccoʼns modified Eagleʼns medium supplemented with 15% fetal bovine serum containing penicillin-streptomycin (100 units/ml and 100 μg/ml) and 71 μm 2-mercaptoethanol. INS-1E (transformed rat β) cells (21Asfari M. Janjic D. Meda P. Li G. Halban P.A. Wollheim C.B. Endocrinology. 1992; 130: 167-178Crossref PubMed Scopus (748) Google Scholar) were grown in RPMI 1640 media supplemented with 10% fetal bovine serum containing penicillin-streptomycin (100 units/ml and 100 μg/ml) as previously described (20Lilla V. Webb G. Rickenbach K. Maturana A. Steiner D.F. Halban P.A. Irminger J.C. Endocrinology. 2003; 144: 1368-1379Crossref PubMed Scopus (116) Google Scholar, 21Asfari M. Janjic D. Meda P. Li G. Halban P.A. Wollheim C.B. Endocrinology. 1992; 130: 167-178Crossref PubMed Scopus (748) Google Scholar). For hGH secretory assays, the cells were transfected with 2 μg of hGH cDNA plus either 6 μg of empty vector (pCDNA 3.1) or the dominant-interfering dynamin mutant (Dyn/K44A) cDNA using Lipofectamine 2000 according to the manufacturerʼns instructions (Invitrogen). For confocal fluorescent microscopy examination, the cells were co-transfected with 2 μg of phogrin-GFP or transferrin receptor cDNAs with Dyk/K44A, respectively. Dynamin 2 siRNA Knockdown and Immunoblotting—Min6B1 cells were grown on and with either 1 of a or siRNA and for The cell were to and with a dynamin 2 dynamin and a as an Min6B1 cell and mouse were with dynamin 1 and dynamin 2 as for dynamin hGH Min6B1 cells were in for to and were for an The cells were in KCl, 1 and bovine serum containing glucose for 2 and in a (20Lilla V. Webb G. Rickenbach K. Maturana A. Steiner D.F. Halban P.A. Irminger J.C. Endocrinology. 2003; 144: 1368-1379Crossref PubMed Scopus (116) Google Scholar). of the the cells were in containing glucose for and the was to containing either glucose, or a of multiple glucose, 1 and The release of hGH into the medium was by an Insulin Min6B1 cells were transfected by with 1 of either the or siRNA for The cells were in containing glucose for 2 and with glucose for an 1 The release of insulin into the medium and insulin content in the were by an of cell of the was used to in cell membrane capacitance as previously described M. E. PubMed Scopus Google Scholar, Y.M. Sheu L. J. Tsushima Gaisano H.Y. Diabetes. 2005; 54: PubMed Scopus (50) Google Scholar). were with to the and from to were with the 1 and with The 4 KCl, 1 2 and with Cell capacitance was by the the of the and a of in the cell M. E. PubMed Scopus Google Scholar). were using an and of from to insulin granule The was at In these the cells were transfected with or to the specific cells for cells were in a with and transfected with and Dyn/K44A. the cells were in containing glucose for 2 and stimulated with either glucose or for 1 the cells were in and with various and dynamin from and For cell Min6B1 cells were with phogrin-GFP in the presence or of siRNA were on or on a for were a using a confocal with and of was for each was with as described results were as and using were using in Insulin to the is following fusion of with the plasma membrane integral membrane proteins are into the membrane and are readily at the cell surface by For the insulin of translocation in or of translocation in cells results in the of these proteins to the plasma membrane G. G. Pessin J.E. J. Physiol. 2005; Scholar). the integral insulin granule membrane protein phogrin as a fusion as previously M. Nakamichi Y. T. H. H. Nagamatsu S. Biochem. J. 2002; PubMed Scopus Google Scholar), we a with insulin containing insulin granules Although phogrin co-localized with these insulin granules, glucose the resulted in any of phogrin to the cell surface membrane These data indicate that the insulin granule membrane protein phogrin did not undergo fusion with the plasma membrane insulin granule we also cell of Min6B1 cells expressing phogrin-GFP These that granules are in but that does not the rate of or the of phogrin at the cell Together, these data are consistent with that the release of insulin occurs by a kiss and run or the mixing of insulin granule membrane with the plasma membrane (17Tsuboi T. McMahon H.T. Rutter G.A. J. Biol. Chem. 2004; 279: 47115-47124Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar). membrane proteins are to undergo from to at phogrin does to the plasma inhibition of endocytosis in an of phogrin at the cell phogrin translocation to the plasma we examined the effect of plasma membrane endocytosis on the cell surface of phogrin In the basal co-expression of the dominant-interfering dynamin mutant (Dyn/K44A) had no effect on the of phogrin more glucose in the presence of Dyn/K44A also did not in any of phogrin that Dyn/K44A inhibited plasma membrane endocytosis, the cells were with transferrin receptor plus either empty vector or Dyn/K44A. these of the transferrin receptor at the cell surface at 4 °C following by the cells to 37 °C for resulted in the of the transferrin receptor a and in the presence of Dyn/K44A the of the transferrin receptor was inhibited and These data although inhibition of endocytosis by Dyn/K44A results in the of membrane proteins as transferrin receptor at the cell there was no effect on the cell surface localization of the insulin granule marker of Insulin described phogrin did not at the plasma membrane endocytosis was we examined the effect of Dyn/K44A on insulin secretion Min6B1 cells were co-transfected with either the empty vector or Dyn/K44A plus a hGH, previous studies have that hGH functions as a marker of insulin secretion S. T. R. Mol. Endocrinol. 2004; PubMed Scopus Google Scholar, M. R. Wollheim C.B. 2000; PubMed Scopus (60) Google Scholar) for secretion from cells to of Dyn/K44A had no effect on basal release of hGH with cells of cells resulted in an increase in hGH release. By contrast, expression of Dyn/K44A the of glucose-stimulated hGH release that resulted in an increase in secretion. any in the of growth hormone content The inhibition of glucose-stimulated hGH release in the media have resulted from a in either first phase secretion and/or second phase secretion. the effect of Dyn/K44A on the of insulin secretion, we examined the of hGH secretion in transfected Min6B1 cells that were to In glucose resulted in a rapid in the rate of hGH release that was at and to Although these cells not a glucose-stimulated second phase secretion, a small was that second phase secretion. Consistent with the secretion expression of Dyn/K44A the initial and the of insulin secretion. was specific to glucose or a for multiple we examined the effect of depolarization In a first phase release of hGH that was also by and basal secretory levels by for glucose cells expressing Dyn/K44A a marked in the and rate of hGH release. insulin secretion first phase release S. M. Diabetes. PubMed Scopus Google Scholar), these data indicate that expression of Dyn/K44A first and second phase insulin secretion. also the expression of Dyn/K44A insulin secretion stimulated by a of multiple secretagogues. The and is a of first and second phase insulin secretion in Min6B1 cells G. R. S. Hays L. H. Rhodes C.J. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus (80) Google Scholar). the combination of in the a increase in the rate of insulin secretion with an to the effect on and hGH secretion, expression of Dyn/K44A inhibited initial and of hGH secretion. of the the indicated that Dyn/K44A inhibited glucose, KCl, and the to similar and Together, these data that in the presence of Dyn/K44A there is a marked inhibition of secretagogue-stimulated granule content Dynamin for with the dynamin function was for the release of granule we that at a macroscopic the of granules in the presence of Dyn/K44A of membrane content to the plasma we the in plasma membrane capacitance following a of by Min6B1 cells were to we first Dyn/K44A secretagogue-stimulated secretion from the INS-1E β-cell that is more to Although cell does not a glucose-stimulated insulin secretion, it is to the for the Min6B1 resulted in a marked increase in hGH secretion in the empty vector and co-transfected there was a inhibition of hGH secretion in the INS-1E cells transfected with Dyn/K44A to the Min6B1 the inhibition of secretion any in the hGH content the similar in INS-1E we examined the in plasma membrane capacitance following a of by serial depolarization membrane capacitance in cells that to following multiple the effect of dynamin we transfected cells with and Dyn/K44A containing a to the transfected cell of also resulted in membrane capacitance following to that for the INS-1E cells in marked contrast, there was a complete inhibition of the depolarization of membrane capacitance increase results are in and that Dyn/K44A results in a in increase in membrane capacitance consistent with a in insulin granule fusion. Dynamin Knockdown Insulin the data were from of a dominant-interfering dynamin mutant and with hGH as an insulin secretion we examined the effect of of dynamin on insulin secretion. is that dynamin 1 is in dynamin 2 is and dynamin expression is to the with low levels in the and R. T. Proc. Natl. Acad. Sci. U. S. A. 1997; PubMed Scopus Google Scholar). β-cells are we examined the expression of the dynamin in the Min6B1 in dynamin 1 was readily in mouse with no expression in Min6B1 cells By contrast, with the dynamin 2 the presence of dynamin 2 in Min6B1 cell with low levels in the mouse dynamin 2 was more in the Min6B1 the cells were transfected with either a siRNA or a dynamin siRNA following there was an of dynamin 2 protein levels with the cells 1 and The of dynamin 2 protein was as protein levels Moreover, with a dynamin that dynamin an of dynamin protein with the dynamin These data that dynamin 2 is the isoform in Min6B1 cells and that the dynamin siRNA was in dynamin protein the of the dynamin 2 siRNA, we the effect of dynamin protein on glucose-stimulated insulin secretion. The dynamin 2 had no effect on basal release of insulin with cells In glucose resulted in an increase in insulin release. By contrast, the knockdown of dynamin 2 the of glucose-stimulated insulin release and resulted in an increase of insulin secretion. any in the of insulin content to the expression of we also did not any of phogrin-GFP in the Dynamin siRNA knockdown cells either in or by cell and Together, these data a for dynamin function in the of insulin secretion granule Various studies have suggested that insulin granules undergo complete fusion resulting in the mixing of granule membrane proteins and lipids with the plasma membrane (12Orci L. Amherdt M. Malaisse-Lagae F. Rouiller C. Renold A.E. Science. 1973; 179: 82-84Crossref PubMed Scopus (60) Google Scholar, 13Takahashi N. Kishimoto T. Nemoto T. Kadowaki T. Kasai H. Science. 2002; 297: 1349-1352Crossref PubMed Scopus (228) Google Scholar, 14Ma L. Bindokas V.P. Kuznetsov A. Rhodes C. Hays L. Edwardson J.M. Ueda K. Steiner D.F. Philipson L.H. Proc. Natl. Acad. Sci. U. S. A. 2004; 101: 9266-9271Crossref PubMed Scopus (83) Google Scholar). Alternatively, other studies have suggested that the insulin granules a fusion pore to intraluminal to followed by membrane process either (kiss and run) or selective (cavicapture) that granule membrane either or from the plasma (17Tsuboi T. McMahon H.T. Rutter G.A. J. Biol. Chem. 2004; 279: 47115-47124Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar, 18Tsuboi T. Zhao C. Terakawa S. Rutter G.A. Curr. Biol. 2000; 10: 1307-1310Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar, 19Taraska J.W. Perrais D. Ohara-Imaizumi M. Nagamatsu S. Almers W. Proc. Natl. Acad. Sci. U. S. A. 2003; 100: 2070-2075Crossref PubMed Scopus (303) Google Scholar, V. Webb G. Rickenbach K. Maturana A. Steiner D.F. Halban P.A. Irminger J.C. Endocrinology. 2003; 144: 1368-1379Crossref PubMed Scopus (116) Google Scholar). More recently, confocal and microscopy of insulin granule the presence of plasma membrane that to undergo fusion (6Ohara-Imaizumi M. Nishiwaki C. Nakamichi Y. Kikuta T. Nagai S. Nagamatsu S. Diabetologia. 2004; 47: 2200-2207Crossref PubMed Scopus (50) Google Scholar, 13Takahashi N. Kishimoto T. Nemoto T. Kadowaki T. Kasai H. Science. 2002; 297: 1349-1352Crossref PubMed Scopus (228) Google Scholar, 14Ma L. Bindokas V.P. Kuznetsov A. Rhodes C. Hays L. Edwardson J.M. Ueda K. Steiner D.F. Philipson L.H. Proc. Natl. Acad. Sci. U. S. A. 2004; 101: 9266-9271Crossref PubMed Scopus (83) Google Scholar, M. Almers W. Curr. Cell Biol. PubMed Scopus Google Scholar, D. Almers W. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). By contrast, microscopy of insulin granule membrane proteins indicated although small proteins and synaptotagmin were into the plasma the granule membrane protein phogrin was from the plasma membrane and (17Tsuboi T. McMahon H.T. Rutter G.A. J. Biol. Chem. 2004; 279: 47115-47124Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar). Moreover, the insulin granule fluorescent protein, was the small fluorescent was that insulin release resulted from the transient opening of a selective fusion pore (17Tsuboi T. McMahon H.T. Rutter G.A. J. Biol. Chem. 2004; 279: 47115-47124Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar, 19Taraska J.W. Perrais D. Ohara-Imaizumi M. Nagamatsu S. Almers W. Proc. Natl. Acad. Sci. U. S. A. 2003; 100: 2070-2075Crossref PubMed Scopus (303) Google Scholar, T. K. M. K. A. 2002; 20: PubMed Scopus Google Scholar). Consistent with these we have also that the of phogrin into the plasma membrane following glucose is by in to phogrin in other membrane proteins undergo plasma membrane at of For and are to the but to and from the plasma membrane J. Cell Biol. PubMed Scopus Google Scholar, S. T. T. T. K. K. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus (116) Google Scholar, B. M. G. Mol. Biol. PubMed Scopus Google Scholar). is readily by the inhibition of plasma membrane endocytosis that results in at the plasma we that phogrin to the plasma membrane it endocytosis was blocked by the expression of the dominant-interfering dynamin inhibition of plasma membrane endocytosis, as by transferrin receptor did not in any cell surface of phogrin in either the basal or These results indicate that insulin granules did not undergo fusion with the plasma and are consistent with a selective of fusion pore opening with a of granule membrane mixing with the plasma More expression of Dyn/K44A or the dynamin 2 knockdown the of insulin secretion stimulated by glucose, KCl, and a combination of multiple secretagogues. of the of insulin release that first and second phase insulin secretion was In with these on insulin secretion, the increase in membrane capacitance was also in the presence of Dyn/K44A. Although data were to between first and second phase insulin secretion, the effect of dynamin function on secretory granule release has previously been in cells by using with of A. Full Text Full Text PDF PubMed Scopus Google Scholar). These results that the of release following of suggesting a effect on second phase secretion. In any case, dynamin is to function in the is that the of granule exocytosis is to endocytosis in a to of the plasma membrane surface Although is an dynamin has recently been to undergo to the of insulin other proteins as and are not (17Tsuboi T. McMahon H.T. Rutter G.A. J. Biol. Chem. 2004; 279: 47115-47124Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar). Moreover, insulin granules are it is that granule occurs a these dynamin is to function in endocytosis, another mechanism for its in the of insulin release. In an secretory model has been proposed in insulin granules are into a the plasma exocytosis (15Leung Y.M. Sheu L. Kwan E. Wang G. Tsushima R. Gaisano H. Biochem. Biophys. Res. Commun. 2002; 292: 980-986Crossref PubMed Scopus (33) Google Scholar, L. W. Diabetes. PubMed Scopus Google Scholar, K. M. Gromada J. Rorsman P. 2000; PubMed Scopus (45) Google Scholar). the plasma membrane granules and the fusion the granules fusion that and granule to the and a leading to the plasma In fusion dynamin not function in endocytosis but the of fusion between compound exocytosis model is also it for the between a increase in membrane capacitance plasma membrane and the kiss and In the kiss and run the initial release phase membrane capacitance to however, following of the transient fusion membrane capacitance and to the basal state in to the in first and second phase insulin secretion. the in membrane capacitance through each depolarization suggesting a of membrane consistent with a complete fusion and The compound exocytosis model for for a single granule the fusion pore and but at the macroscopic the multiple and in a increase in membrane surface Moreover, also for the of a small of granule proteins to into the plasma membrane but the of the granule protein proteins to it is to that microscopy of single granule fusion events was to by the expression of a dominant-interfering dynamin mutant T. Terakawa S. B.A. C. J. A. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). In to data a marked in the of insulin secretion. These are similar to for granule release in T. H. T. J. E. M. Full Text Full Text PDF PubMed Scopus Google Scholar). In single granule release events have and in the and however, the of granule release events is in the of These in macroscopic events may the specific in insulin secretion. The is the presence of fusion that granule is for the empty insulin granule to from the fusion for the of a insulin Li for with

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