Calcium-activated potassium channels in the endothelium of intact rat aorta

Abstract

1. Single K+ channel currents and membrane potential were recorded in the endothelium of excised intact rat aorta. 2. Two types of K+ channel were found in excised patches, K(Ch) and K(Ap). With Na+ and K+ as the main external and internal cations, outward conductances were 6.7 pS (K(Ch)) and 2.8 pS (K(Ap)). In symmetric 150 mM K+, the inward conductances were 18 and 9.1 pS. 3. Activation by Ca2+ was concentration dependent. K(Ch) channels were activated by [Ca2+] > 0.1 μM and K(Ap) by [Ca2+] > 0.5 μM. 4. Apamin at concentrations > 1 nM inhibited K(Ap) channels. Block was complete at 10 nM. K(Ap) channels were insensitive to charybdotoxin. K(Ch) channels were inhibited by charybdotoxin at concentrations > 50 nM, but were insensitive to apamin. 5. d-Tubocurarine (dTC)) evoked flickering activity of K(Ap) channels at concentrations > 5 μM and complete block at 100 μM. At these doses, dTC did not affect K(Ch) channels, but at concentrations > 1 mM it decreased the single channel amplitude. 6. Hyperpolarization evoked by acetylcholine was unaffected by apamin or dTC at low concentrations (≤ 100 μM), but inhibited by high concentrations of charybdotoxin (> 50 nM) or dTC (> 1 mM). 7. These data suggest that K(Ch) channels are novel Ca2+-activated K+ channels responsible for the ACh-evoked hyperpolarization in the endothelium of rat aorta.