Mechanisms underlying regional differences in the Ca²⁺sensitivity of BK_Cacurrent in arteriolar smooth muscle

Key points The plasma membrane large‐conductance Ca2+‐activated, K+channel (BKCa) is a major ion channel contributing to the regulation of membrane potential. Activation of large‐conductance Ca2+‐activated K+channel by both depolarization and increased intracellular Ca2+results in hyperpolarization that acts to limit agonist and mechanically induced vasoconstriction in small arteries. Using patch‐clamp techniques we demonstrate that regional differences exist in how BKCais regulated, particularly with respect to its Ca2+sensitivity. Using single‐channel recordings and siRNA to manipulate protein subunit expression, it is argued that the β1‐subunit plays a more dominant role in cerebral blood vessels as compared with small arteries from skeletal muscle. Subtle differences in the regulation of membrane potential in different vascular beds allow local blood flow and pressure to be closely adapted to the tissue's metabolic needs. Abstract β1‐Subunits enhance the gating properties of large‐conductance Ca2+‐activated K+channels (BKCa) formed by α‐subunits. In arterial vascular smooth muscle cells (VSMCs), β1‐subunits are vital in coupling SR‐generated Ca2+sparks to BKCaactivation, affecting contractility and blood pressure. Studies in cremaster and cerebral VSMCs show heterogeneity of BKCaactivity due to apparent differences in the functional β1‐subunit:α‐subunit ratio. To define these differences, studies were conducted at the single‐channel level while siRNA was used to manipulate specific subunit expression. β1 modulation of the α‐subunit Ca2+sensitivity was studied using patch‐clamp techniques. BKCachannel normalized open probability (NPo)versusmembrane potential (Vm) curves were more left‐shifted in cerebralversuscremaster VSMCs as cytoplasmic Ca2+was raised from 0.5 to 100 μm. CalculatedV1/2values of channel activation decreased from 72.0 ± 6.1 at 0.5 μmCa2+ito −89 ± 9 mV at 100 μmCa2+iin cerebral compared with 101 ± 10 to −63 ± 7 mV in cremaster VSMCs. Cremaster BKCachannels thus demonstrated an ∼2.5‐fold weaker apparent Ca2+sensitivity such that at a value ofVmof −30 mV, a mean value of [Ca2+]iof 39 μmwas required to open half of the channels in cremasterversus16 μm[Ca2+]iin cerebral VSMCs. Further, shortened mean open and longer mean closed times were evident in BKCachannel events from cremaster VSMCs at either −30 or 30 mV at any given [Ca2+]. β1‐Subunit‐directed siRNA decreased both the apparent Ca2+sensitivity of BKCain cerebral VSMCs and the appearance of spontaneous transient outward currents. The data are consistent with a higher ratio of β1‐subunit:α‐subunit of BKCachannels in cerebral compared with cremaster VSMCs. Functionally, this leads both to higher Ca2+sensitivity andNPofor BKCachannels in the cerebral vasculature relative to that of skeletal muscle.

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.