Electrical and Mechanical Responses to Endothelin in Small Arteries of the Dog Kidney

The contractile response of renal arterial muscle to porcine endothelin (ET-1) was studied by measuring vessel diameters and vascular smooth muscle transmembrane potentials in small arteries (300–600 μm inside diameter) isolated from dog kidneys and cannulated with micropipettes connected to a pressurized reservoir system. Endothelin (10−12 to 10−8 M) was a potent constrictor of these vessels and caused a concentration-dependent contraction at a mean EC50 (median effective concentration) of 3.1 (±1.15) × 10−10 M. Endothelin also produced a modest depolarization of arterial smooth muscle much smaller than had previously been demonstrated to occur in these vessels in response to norepinephrine or transmural pressure elevation. Endothelin-induced contractions were partially inhibited by 10−6 M nifedipine and abolished by Ca2+ -free solution. Although the influx of extracellular Ca2+ ions through dihydropyridine-sensitive pathways contributes to endothelin-induced contractions of these vessels, electromechanical coupling does not appear to be the sole determinant of the magnitude of endothelin-induced constriction in canine small renal arteries.