Characterization of enhanced 45Ca2+ efflux in cultured vascular smooth muscle cells from spontaneously hypertensive rats.
In this study we have compared Ca2+ efflux in cultured aortic smooth muscle cells derived from male, 10-week-old spontaneously hypertensive and Wistar-Kyoto rats. The role of Ca(2+)-dependent protein kinase C and Ca2+ uptake in the regulation of the Ca2+ pump and Na(+)-Ca2+ exchange mediated Ca2+ efflux were investigated. Basal, angiotensin II, and ionomycin-stimulated Ca2+ effluxes were significantly higher in spontaneously hypertensive rats. Brief (5 min) or prolonged (3 h) incubation of the cells with 100 nmol/L 12-O-tetradecanoylphorbol-13-O-acetate (TPA), a protein kinase C stimulator, did not significantly affect the maximum Ca2+ efflux rate in either strain. However, the Ca2+ efflux rates at early timepoints in Wistar-Kyoto rats were increased by TPA, but not in spontaneously hypertensive rats. Incubation of cells with [45Ca]-labeled CaCl2 in balanced salt solution for 4 h led to greater Ca uptake in spontaneously hypertensive rats compared to Wistar-Kyoto controls. Verapamil (1 mumol/L) for 4 h reduced the cellular Ca content of spontaneously hypertensive rats by 30% to the level of Wistar-Kyoto rats; it also reduced the Ca content in Wistar-Kyoto rats, but to a lesser extent (18%). In parallel, Ca2+ efflux was also reduced by verapamil to a greater extent in spontaneously hypertensive rats than in Wistar-Kyoto rats. We conclude that Ca2+ efflux was enhanced in spontaneously hypertensive rats by a mechanism partly associated with greater Ca2+ uptake by a verapamil-sensitive pathway and possibly an alteration of protein kinase C regulation. However, an up-regulation of the number or efficiency of Ca2+ efflux sites may also significantly contribute as an adaptive response to enhanced Ca2+ influx.
Chen
S
S
Department of Pharmacy, University of Sydney, New South Wales, Australia.
Monteith
G R
GR
Roufogalis
B D
BD
D000818:Animals; D002118:Calcium / Q000819:agonists / Q000378:metabolism* / Q000493:pharmacokinetics; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002132:Calcium Radioisotopes; D002478:Cells, Cultured; D006973:Hypertension / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D015759:Ionomycin / Q000494:pharmacology; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D011918:Rats, Inbred SHR; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; D002132:Calcium Radioisotopes; D015759:Ionomycin; D014700:Verapamil; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium