Newborn rat distal cells express an apical Ca<sup>2+</sup> channel activated by dihydropyridine drugs. Similarly, in Madin-Darby canine kidney (MDCK) cells, nifedipine increased Ca<sup>2+</sup><sub>i</sub> in a concentration-dependent manner (IC<sub>50</sub> = 4 µ<i>M</i>) in fura-2-loaded cells. Response to nifedipine was abolished by EGTA, suggesting that it depends on extracellular calcium. Ca<sup>2+</sup> channel antagonist isradipine and agonist BayK8644 increased Ca<sup>2+</sup><sub>i</sub> indicating that this effect is related to the dihydropyridine group. Diltiazem (20 µ<i>M</i>) and gadolinium (200 µ<i>M</i>) decreased the nifedipine effect (62 and 43%, respectively). Lanthanum (100 µ<i>M</i>) did not change the response. Valinomycin clamping of the membrane potential did not modify nifedipine-induced increment, indicating that it was unrelated to potassium fluxes. We performed whole cell clamp experiments in MDCK cells maintained at –50 mV with perfusion solution containing 10 m<i>M</i> CaCl<sub>2</sub>. Nifedipine (20 µ<i>M</i>) induced an increase in current (1.2 ± 0.3 nA), which was partially inhibited by Gd<sup>3+</sup>. No significant current was induced by nifedipine in the presence of 0.5 m<i>M</i> EGTA. To determine the effects of nifedipine on the membrane potential, we performed oxonol fluorescence experiments. The addition of nifedipine or Bay K8644 induced depolarization, highly dependent on external sodium. Nifedipine (20 µ<i>M</i>) induced depolarization of 6.9 ± 0.8 mV (n = 21). EC<sub>50</sub> to nifedipine was in the 10 µ<i>M</i> range. We conclude that MDCK cells exhibit a dihydropyridine-activated cationic channel.