The signaling pathways of endothelin-1 (ET-1) mediated vasoconstriction in the renal circulation have not been elucidated but appear to be distinct between ET_A and ET_B receptor 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 ET_B 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 inserted into the renal artery for drug infusion. All rats were given either 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 all groups). Both 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 bi-phasic Ca²⁺ response while S6c had no effect on cytosolic Ca²⁺. Furthermore, Ca²⁺ channel blockade (diltiazem or nickel) had no effect on either 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.