Jf. Quignard et al., Role of endothelial cell hyperpolarization in EDHF-mediated responses in the guinea-pig carotid artery, BR J PHARM, 129(6), 2000, pp. 1103-1112
1 Experiments were performed to identify the potassium channels involved in
the acetylcholine-induced endothelium-dependent hyperpolarization of the g
uinea-pig internal carotid artery. Smooth muscle and endothelial cell membr
ane potentials were recorded in isolated arteries with intracellular microe
lectrodes. Potassium currents were recorded in freshly-dissociated smooth m
uscle cells using patch clamp techniques.
2 In single myocytes, iberiotoxin (0.1 mu M)-, charybdotoxin (0.1 mu M)-, a
pamin (0.5 mu M)- and 4-aminopyridine (5 mM)-sensitive potassium currents w
ere identified indicating the presence of large- and small-conductance calc
ium-sensitive potassium channels (BKCa and SKCa) as well as voltage-depende
nt potassium channels (K-V) Charybdotoxin and iberiotoxin inhibited the sam
e population of BKCa but a conductance specifically sensitive to the combin
ation of charybdotoxin plus apamin could not be detected. 4-aminopyridine (
0.1-25 mM) induced a concentration-dependent inhibition of K-V without affe
cting the iberiotoxin- or the apamin-sensitive currents.
3 In isolated arteries, both the endothelium-dependent hyperpolarization of
smooth muscle and the hyperpolarization of endothelial cells induced by ac
etylcholine or by substance P were inhibited by 5 mM 4-aminopyridine.
4 These results indicate that in the vascular smooth muscle cells of the gu
inea-pig carotid artery, a conductance specifically sensitive to the combin
ation of charybdotoxin plus apamin could not be detected, comforting the hy
pothesis that the combination of these two toxins should act on the endothe
lial cells. Furthermore, the inhibition by 4-aminopyridine of both smooth m
uscle and endothelial hyperpolarizations, suggests that in order to observe
an endothelium-dependent hyperpolarization of the vascular smooth muscle c
ells, the activation of endothelial potassium channels is likely to be requ
ired.