Inhibition of the cardiac protein kinase A-dependent chloride conductance by endothelin-1

Endothelin-1 is a peptide hormone constitutively secreted by vascular and endocardial endothelial cells^1-3. Secretion of endothelin-1 is increased under certain pathophysiological conditions, including coronary vasospasm, cardiac ischaemia and myocardial infarction. We have examined the effect of endothelin-1 on the protein kinase A (PKA)-dependent chloride current in voltage-clamped guinea pig ventricular myocytes. This conductance, induced by catecholamines through β-adrenergic receptors, counteracts the simultaneously increased L-type calcium current by shortening the action potential duration^4-6. We report here that endothelin-1, acting through ET_A (endothelin-1-selective) receptors, inhibited the current through a pertussis toxin-sensitive mechanism, analogous to muscarinic receptors, by reducing the intracellular cyclic AMP concentration. This effect of endothelin-1 should help protect the ventricle against potentially arrhythmogenic shortening of the action potential during ischaemia when the circulating levels of catecholamines are increased.