Expression and function of native potassium channel (K_vα1) subunits in terminal arterioles of rabbit

1. In this study we investigated the expression and function of the K_Vα1 subfamily of voltage-gated K⁺ channels in terminal arterioles from rabbit cerebral circulation. 2. K⁺ current was measured from smooth muscle cells within intact freshly isolated arteriolar fragments. Current activated on depolarisation positive of about -45 mV and a large fraction of this current was blocked by 3,4-diaminopyridine (3,4-DAP) or 4-aminopyridine (4-AP), inhibitors of K_V channels. Expression of cRNA encoding K_V1.6 in Xenopus oocytes also generated a 4-AP-sensitive K⁺ current with a threshold for activation near -45 mV. 3. Immunofluorescence labelling revealed K_V1.2 to be specifically localised to endothelial cells, and K_V1.5 and K_V1.6 to plasma membranes of smooth muscle cells. 4. K_V channel current in arteriolar fragments was blocked by correolide (which is specific for the K_Vα1 family of K_V channels) but was resistant to recombinant agitoxin-2 (rAgTX2; which inhibits K_V1.6 but not K_V1.5). Heterologously expressed K_V2.1 was resistant to correolide, and K_V1.6 was blocked by rAgTX2. 5. Arterioles that were mildly preconstricted and depolarised by 0.1-0.3 nM endothelin-1 constricted further in response to 3,4-DAP, 4-AP or correolide, but not to rAgTX2. 6. We suggest that K_Vα1 channels are expressed in smooth muscle cells of terminal arterioles, underlie a major part of the voltage-dependent K⁺ current, and have a physiological function to oppose vasoconstriction. K_Vα1 complexes without K_V1.5 appear to be uncommon.