Regulation of the plasma membrane Ca2+ pump by cyclic nucleotides in cultured vascular smooth muscle cells.
We investigated the mechanisms of Ca2+ extrusion from cultured rat aortic smooth muscle cells while monitoring changes in the cytosolic Ca2+ concentration ([Ca2+]i) using fura 2 fluorescence. 45Ca2+ efflux from these cells consisted of two major mechanisms; one was dependent on the extracellular sodium concentration (Na+o) and the other was independent of Na+o. Na+o-dependent efflux increased monotonically with increasing [Ca2+]i between 0.1 and 1.0 microM, whereas Na+o-independent efflux reached a plateau at 0.6-1 microM [Ca2+]i with a half-maximum obtained at about 0.16 microM. At [Ca2+]i below 1 microM, the latter was significantly greater than the former. Unlike the Na+o-dependent mechanism, Na+o-independent 45Ca2+ efflux was inhibited almost entirely by extracellularly added La3+ or a combination of high extracellular pH (pH 8.8) and 20 mM Mg2+. It was also inhibited, although not completely, by compound 48/80, a calmodulin antagonist, and vanadate. These results strongly suggest that Na+o-dependent and Na+o-independent 45Ca2+ effluxes occur via the Na+/Ca2+ exchanger and the ATP-dependent Ca2+ pump, respectively. Sodium nitroprusside and atrial natriuretic factor, which are agents that stimulate intracellular production of cGMP, and 8-BrcGMP significantly accelerated the Na+o-independent 45Ca2+ efflux especially at low [Ca2+]i. Forskolin, dibutyryl cAMP, and 8-Br-cAMP, however, showed no stimulation. These results suggest that the plasma membrane Ca2+ pump is regulated by cGMP but not by cAMP in intact vascular smooth muscle cells.
Furukawa
K
K
Department of Molecular Physiology, National Cardiovascular Center Research Institute, Osaka, Japan.
Tawada
Y
Y
Shigekawa
M
M
D000818:Animals; D009320:Atrial Natriuretic Factor / Q000494:pharmacology; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007811:Lanthanum / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology*; D009599:Nitroprusside / Q000494:pharmacology; D009712:Nucleotides, Cyclic / Q000494:pharmacology*; D051381:Rats; D011921:Rats, Inbred WKY; D012964:Sodium / Q000378:metabolism
D009712:Nucleotides, Cyclic; D009599:Nitroprusside; D005576:Colforsin; C016276:8-bromocyclic GMP; D003994:Bucladesine; D007811:Lanthanum; D009320:Atrial Natriuretic Factor; D012964:Sodium; D000252:Calcium-Transporting ATPases; D006152:Cyclic GMP; D008274:Magnesium; D002118:Calcium