Figure 1.

Potassium channels in smooth muscle cells of the guinea pig carotid artery. Effect of the combination of different inhibitors of potassium channels in freshly isolated smooth muscle cells of the guinea pig carotid artery (whole cell configuration of the patch-clamp technique). (A) Large global currents observed in the presence of intracellular calcium for a ramp depolarization from −100 to +80 mV. This current is partially inhibited by iberiotoxin (IbTx), indicating the presence of calcium-activated potassium channels of large conductance (BK_Ca). The addition of charybdotoxin (ChTx) does not produce any further inhibition, suggesting that neither the calcium-activated potassium channels of intermediate conductance (IK_Ca)-dependent current nor the A-type rapidly inactivating transient outward current (K_TO) is activated. The addition of apamin (Apa) produces a further inhibition, indicating the presence of a calcium-activated potassium channels of small conductance ‘(SK_Ca)-like’ current. The subsequent addition of 4-aminopyridine (4-AP) blocked the remaining global outward current demonstrating the contribution of voltage-activated potassium channels (K_V). (B) Large outward current observed for a step depolarization from −100 to +60 mV, confirming the contribution of BK_Ca, ‘SK_Ca-like’ and K_V channels in the recorded current. The effect of 4-AP is not shown for the sake of clarity. Modified from Quignard et al. (Br J Pharmacol 2000b).