title: New evidence of a dihydropyridine-activated cationic channel in the MDCK cell line.
abstract: Newborn rat distal cells express an apical Ca2+ channel activated by dihydropyridine drugs. Similarly, in Madin-Darby canine kidney (MDCK) cells, nifedipine increased Ca2+i in a concentration-dependent manner (IC50=4 μM) in fura-2-loaded cells. Response to nifedipine was abolished by EGTA, suggesting that it depends on extracellular calcium. Ca2+ channel antagonist isradipine and agonist BayK8644 increased Ca2+i indicating that this effect is related to the dihydropyridine group. Diltiazem (20 μM) and gadolinium (200 μM) decreased the nifedipine effect (62 and 43%, respectively). Lanthanum (100 μM) 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 mM CaCl2. Nifedipine (20 μM) induced an increase in current (1.2±0.3 nA), which was partially inhibited by Gd3+. No significant current was induced by nifedipine in the presence of 0.5 mM 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 μM) induced depolarization of 6.9±0.8 mV (n=21). EC50 to nifedipine was in the 10 μM range. We conclude that MDCK cells exhibit a dihydropyridine-activated cationic channel.
authors.affiliation: Departamento de Farmacia, Escuela Nacional de Ciencias Biológicas del Instituto Politécnico Nacional, México, Mexico.
authors.forename: E
authors.initials: E
authors.lastname: Melendez
authors.forename: M
authors.initials: M
authors.lastname: Bidet
authors.forename: J L
authors.initials: JL
authors.lastname: Reyes
authors.forename: S
authors.initials: S
authors.lastname: Martial
authors.forename: O
authors.initials: O
authors.lastname: Barbier
authors.forename: M
authors.initials: M
authors.lastname: Tauc
authors.forename: E
authors.initials: E
authors.lastname: Sanchez
authors.forename: P
authors.initials: P
authors.lastname: Poujeol
mesh_terms: D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000378:metabolism*; D002412:Cations; D002460:Cell Line; D004095:Dihydropyridines / Q000378:metabolism* / Q000494:pharmacology*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D007668:Kidney / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002412:Cations; D004095:Dihydropyridines; C038806:1,4-dihydropyridine; D009543:Nifedipine