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 hormonal activation. We found that the dihydropyridine (DHP) nifedipine (20 μM) produced an increase in [Ca²⁺]_i from 87.6 ± 3.3 nM to 389.9 ± 29.0 nM 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, neither verapamil nor diltiazem induced any rise in [Ca²⁺]_i. Experiments in the presence of EGTA showed that external Ca²⁺ was required for the nifedipine effect, while lanthanum (20 μM), gadolinium (100 μM), and diltiazem (20 μM) inhibited the effect. Experiments done in the presence of valinomycin resulted in the same nifedipine effect, showing that K⁺ channels were not involved 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 cultures of cells from terminal nephron of newborn rats are a useful tool for investigating Ca²⁺ transport mechanisms during growth, and 2) newborn rat CCD cells in primary culture exhibit a new apical nifedipine-activated Ca²⁺ channel of capacitive type (either transient receptor potential or leak channel).