COMPLEMENT-INDUCED CA2-CHANNEL ANTAGONIST NIFEDIPINE OR BY SOME BIVALENT INORGANIC CATIONS( INFLUX IN CULTURED FIBROBLASTS IS DECREASED BY THE CALCIUM)

The effects of different extracellular cations or organic Ca2+-channel modulators on complement-induced changes in intracellular Ca2+ and ce ll death have been investigated in the transfected NIH-3T3 HIR 3.5 cel l line, which overexpresses the human insulin receptor. Cells were inc ubated with mouse anti-(human insulin receptor) monoclonal antibodies before exposure to rabbit or human serum (sources of heterologous comp lement). Changes in intracellular Ca2+ were complement-dependent (meas ured by influx of Ca-45), as was cytotoxicity (monitored by leakage of lactate dehydrogenase into the culture supernatant). Addition of a di hydropyridine Ca2+-channel antagonist (nifedipine) or some bivalent in organic cations caused inhibition of Ca-45 entry via a novel channel d istinct from endogenous voltage-gated Ca2+ channels. Nifedipine decrea sed, but conversely the addition of a phenylalkylamine Ca2+-channel an tagonist (verapamil) or the inorganic Ca2+ agonists Ba2+ and Sr+ incre ased, complement-induced cytotoxicity. These agents had no effect on c ell viability at the studied concentrations, in the absence of complem ent. It is concluded that complement-induced cytotoxicity is mediated by Ca2+ influx through novel specific transmembrane channels which are sensitive to the Ca2+-channel antagonist nifedipine, but otherwise sh ow little resemblance to L- or T-type voltage-gated Ca2+ channels.