THE PROPERTIES AND DISTRIBUTION OF INWARD RECTIFIER POTASSIUM CURRENTS IN PIG CORONARY ARTERIAL SMOOTH-MUSCLE

1. Whole-cell potassium currents were studied in single smooth muscle cells enzymatically isolated from pig coronary arteries. 2. In cells i solated from small diameter branches of the left anterior descending c oronary artery (LAD), an inward rectifier potassium current (I-K(IR)) was identified, which was inhibited by extracellular barium ions, sugg esting the presence of inward rectifier potassium (K-IR) channels. 3. The conductance for I-K(IR) measured in 6, 12, 60 and 140 mM extracell ular potassium was a function of membrane potential and the extracellu lar potassium concentration. 4. On hyperpolarization, I-K(IR) activate d along an exponential time course with a time constant that was volta ge dependent. 5. Inward rectifier current was compared in cells isolat ed from coronary vessels taken from different points along the vascula r tree. Current density was greater in cells isolated from small diame ter coronary arteries; at -140 mV it was -20.5 +/- 4.4 pA pF(-1) (n = 23) in 4th order branches of the LAD, but -0.8 +/- 0.2 pA pF(-1) (n = 11) in the LED itself. 6. In contrast to I-K(IR), there was little eff ect of arterial diameter on the density of voltage-dependent potassium current; densities at +30 mV were 12.8 +/- 1.3 pA pF(-1) (n = 19) in 4th order branches and 17.4 +/- 3.1 pA pF(-1) (n = 11) in the LAD. 7. We conclude that K-IR channels are present in pig coronary arteries, a nd that they are expressed at a higher density in small diameter arter ies. The presence of an enhanced I-K(IR) may have functional consequen ces for the regulation of cell membrane potential and tone in small co ronary arteries.