Endothelin increases single-channel calcium currents in coronary arterial smooth muscle cells

Endothelin (ET), a newly identified vasoconstrictor peptide produced by endothelial cells, depends on extracellular calcium for its action [(1988) Nature 332, 411-415]. It is not yet known whether the increase in calcium influx induced by ET results from a direct effect on the Ca²⁺ channels or is secondary to a reduction in membrane potential. To address this question, we studied the effects of ET on single-channel calcium currents of freshly dissociated porcine coronary artery smooth muscle cells using the cell-attached mode of the patch-clamp technique. We show that ET increases Cal⁺-channel activity with no effect on channel open time or conductance. The ability of bath-applied ET to increase single-channel calcium currents in the cell-attached mode is evidence that the peptide acts via a second messenger system.