Different 1,4-dihydropyridines exhibit discriminating effects on passive calcium uptake in rat liver plasma membrane vesicles.
The effects of a number of calcium channel effectors on Ca2+ uptake by rat liver plasma membrane vesicles was examined. Nifedipine, verapamil and diltiazem had to be present at 1 mM in order to produce > 50% inhibition of Ca2+ uptake. The two structurally similar 1,4-dihydropyridines, nicardipine and nisoldipine exhibited opposite effects; nicardipine inhibited while nisoldipine stimulated Ca2+ uptake. The results show that low concentrations (microM) of calcium channel blockers of excitable cells have little effect on Ca2+ uptake by liver plasma membrane vesicles consistent with earlier findings of others that voltage-gated calcium channels are absent in hepatocytes. However, the opposite effects of higher concentrations (ca. 1 mM) of nicardipine and nisoldipine on Ca2+ uptake suggest a discriminatory action that might be useful in studying further the mechanism of passive Ca2+ uptake by these membrane vesicles.
Cromer
B
B
Division of Biochemistry and Molecular Biology, School of Life Sciences, Australian National University, Canberra.
Bygrave
F L
FL
D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects*; D002462:Cell Membrane / Q000187:drug effects; D004095:Dihydropyridines / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051381:Rats; D017208:Rats, Wistar
D015220:Calcium Channels; D004095:Dihydropyridines; D002118:Calcium