An ATP, calcium and voltage sensitive potassium channel in porcine coronary artery smooth muscle cells

There is increasing interest in the roles played by potassium channels of smooth muscle in protecting against ischemic and anoxic insults. Hence, potassium-selective channels were studied in freshly dispersed porcine coronary artery smooth muscle cells using the inside-out variant of the patch-clamp technique. The most abundant potassium channel had a conductance of 148 pS in a 5.4 140 mM K⁺ gradient, at 0 mV, and was regulated by cytoplasmic ATP (0.05 - 3.0 mM), cytoplasmic Ca²⁺ (0.1-10 μM) and voltage. ATP and AMP-PNP (0.5 mM) reduced the probability of channel opening (P₀) by 87 and 92%, respectively. This inhibition was partially reversed by the addition of 0.5 mM ADP. ADP on its own (2 mM) reduced P₀ by 46%. It appears, therefore, that this channel shares properties with both the ATP-sensitive and the calcium-regulated potassium channels, raising the possibility that it plays a central role in the regulation of coronary blood flow.