Nifedipine-activated Ca2+ permeability in newborn rat cortical collecting duct cells in primary culture

To characterize Ca2+ transport in newborn rat cortical collecting duct (CCD ) cells, we used nifedipine, which in adult rat distal tubules inhibits the intracellular Ca2+ concentration ([Ca2+](i)) increase in response to hormo nal activation. We found that the dihydropyridine (DHP) nifedipine (20 muM) produced an increase in [Ca2+](i) from 87.6 +/- 3.3 nM to 389.9 +/- 29.0 n M in 65% of the cells. Similar effects of other DHP (BAY K 8644, isradipine ) were also observed. Conversely, DHPs did not induce any increase in [Ca2](i) in cells obtained from proximal convoluted tubule. In CCD cells, neith er verapamil nor diltiazem induced any rise in [Ca2+](i). Experiments in th e presence of EGTA showed that external Ca2+ was required for the nifedipin e effect, while lanthanum (20 mM), gadolinium (100 mM), and diltiazem (20 m M) inhibited the effect. Experiments done in the presence of valinomycin re sulted in the same nifedipine effect, showing that K+ channels were not inv olved in the nifedipine-induced [Ca2+](i) rise. H2O2 also triggered [Ca2+]( i) rise. However, nifedipine-induced [Ca2+](i) increase was not affected by protamine. In conclusion, the present results indicate that 1) primary cul tures of cells from terminal nephron of newborn rats are a useful tool for investigating Ca2+ transport mechanisms during growth, and 2) newborn rat C CD cells in primary culture exhibit a new apical nifedipine-activated Ca2channel of capacitive type (either transient receptor potential or leak cha nnel).