Figure 6.
Involvement of SKCa and IKCa in EDHF-mediated responses. Endothelium-dependent hyperpolarizations to ACh in vascular smooth muscle of the guinea pig carotid artery (in the presence of inhibitors of NOS and COX). (A) Original membrane potential recordings showing the concentration-dependent hyperpolarizing effect of ACh. (B) The concentration- and endothelium-dependent hyperpolarizations produced by ACh are not affected by the presence of ChTx, partially inhibited by that of Apa. and virtually abolished by the combination of the two toxins. (C) Similarly, TRAM-34, a non-peptidic and selective blocker of IKCa, does not affect the hyperpolarization elicited by ACh while UCL 1684, a selective blocker of SKCa, produces a partial inhibition. The combination of the two blockers prevents the hyperpolarizing effect of ACh. Modified from Gluais et al. (Br J Pharmacol, 2005). ACh, acetylcholine; Apa., apamin; ChTx, charybdotoxin; COX, cyclooxygenase; EDHF, endothelium-derived hyperpolarizing factor; IKCa, calcium-activated potassium channels of intermediate conductance; NOS, nitric oxide synthase; SKCa, calcium-activated potassium channels of small conductance.