Characterization and localization of Ac-SDKP receptor binding sites using<sup>125</sup>I-labeled Hpp-Aca-SDKP in rat cardiac fibroblasts
Bibliographic record
Abstract
We have shown that the tetrapeptide N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) inhibited endothelin-1 (ET-1)-induced cell proliferation and collagen synthesis in cultured rat cardiac fibroblasts (CFs) and reduced left ventricle collagen deposition in rats with aldosterone (salt)- and ANG II-induced hypertension. However, it is not known whether these effects are mediated by receptor binding sites specific for Ac-SDKP. We hypothesized that Ac-SDKP exerts antifibrotic effects by binding to specific receptor sites in cultured rat CFs, which mediate the inhibitory effects of Ac-SDKP on ET-1-stimulated collagen synthesis. Ac-SDKP binding sites in rat CFs and hearts were characterized by a specific radioligand, (125)I-labeled 3-(p-hydroxyphenyl)-propionic acid (or desaminotyrosine) (Hpp)-Aca-SDKP, a biologically active analog of Ac-SDKP. (125)I-labeled Hpp-Aca-SDKP bound to rat CFs and fractionated membranes with similar affinities and specificity in a concentration- and time-dependent fashion. Scatchard plot analyses revealed a single class of high-affinity Hpp-Aca-SDKP binding sites (maximal binding: 1,704 +/- 198 fmol/mg protein; dissociation constant: 3.3 +/- 0.6 nM). (125)I-labeled Hpp-Aca-SDKP binding in CFs was displaced by unlabeled native peptide Ac-SDKP (inhibition constant: 0.69 +/- 0.15 nM) and the analog Hpp-Aca-SDKP (inhibition constant: 10.4 +/- 0.2 nM) but not the unrelated peptide ANG II or ET-1 (10 microM). In vitro, both Ac-SDKP and Hpp-Aca-SDKP inhibited ET-1-stimulated collagen synthesis in CFs in a dose-dependent fashion, reaching a maximal effect at 1 nM (control: 7.5 +/- 0.4, ET-1: 19.9 +/- 1.2, ET-1+SDKP: 7.7 +/- 0.4, ET-1+Hpp-Aca-SDKP: 9.7 +/- 0.1 microg/mg protein; P < 0.001). Ac-SDKP also significantly attenuated ET-1-induced increases in intracellular calcium and MAPK ERK1/2 phosphorylation in CFs. In the rat heart, in vitro autoradiography revealed specific (125)I-labeled Hpp-Aca-SDKP binding throughout the myocardium, primarily interstitially. We believe that these results demonstrate for the first time that Hpp-Aca-SDKP is a functional ligand specific for Ac-SDKP receptor binding sites and that both Ac-SDKP and Hpp-Aca-SDKP exert antifibrotic effects by binding to Ac-SDKP receptors in rat CFs.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".