The signaling pathways of endothelin (ET)-1-mediated vasoconstriction in the renal circulation have not been elucidated but appear to be distinct between ETA and ETB receptors. The purpose of this study was to determine the role of L-type Ca2+ channels in the vasoconstrictor response to ET-1 and the ETB receptor agonist sarafotoxin 6c (S6c) in the rat kidney. Renal blood flow (RBF) was measured with an ultrasonic flow probe in anesthetized rats, and a microcatheter was inserted into the renal artery for drug infusion. All rats were given vehicle (0.9% NaCl) or three successive bolus injections (1, 10, and 100 pmol) of ET-1 or S6c at 30-min intervals (n = 6 in each group). ET-1 and S6c produced dose-dependent decreases in RBF. The Ca2+ channel blocker nifedipine (1.5 μg) significantly attenuated the RBF response only at the highest doses of ET-1 and S6c. In the isolated blood-perfused juxtamedullary nephron preparation, Ca2+ channel blockade with diltiazem had a very small inhibitory effect on ET-1-induced decreases in afferent arteriolar diameter only at the lowest concentrations of ET-1. In vascular smooth muscle cells isolated from preglomerular vessels, ET-1 produced a typical biphasic Ca2+ response, whereas S6c had no effect on cytosolic Ca2+. Furthermore, Ca2+ channel blockade (diltiazem or Ni2+) had no effect on the peak or sustained increase in cytosolic Ca2+ produced by ET-1. These results support the hypothesis that L-type Ca2+ channels play only a minor role in the constrictor responses to ET-1 in the renal microcirculation. Copyright © 2005 the American Physiological Society.