The regulation of the cytoplasmic free Ca2+ concentration in aortic smooth muscle cells (A7r5 line) after stimulation by vasopressin and bombesin.
The characteristics of intracellular Ca2+ transient induced by vasopressin and bombesin in aortic smooth muscle cells were studied using flow cytometric analysis of indo-1 loaded cells. The two hormones induced a rapid and transient rise in [Ca2+]i. This Ca2+ transient was independent of the presence of extracellular Ca2+. Addition of bombesin to cells that have already been stimulated by vasopressin (or conversely the addition of vasopressin to bombesin-stimulated cells) results in a second Ca2+ transient that has a smaller amplitude. This transient is the same when the external Ca2+ concentration is lowered from 1.8 mM to 50 nM, suggesting that the agonist-sensitive pool reloaded using the Ca2+ that has been previously released into the cytoplasm. Intracellular Ca2+ pools that have been depleted by a prolonged incubation of the cells in a low Ca2+ medium can be refilled by shifting cells to a high Ca2+ medium. The reloading was analyzed in detail and found to be a slow process. It is hardly affected by Ni2+ or by (-)D888, a potent inhibitor of the voltage-dependent Ca2+ channels. It is accelerated when Ca2+ uptake by the Na+/Ca2+ exchange system is stimulated. The results suggest that Ca2+ homeostasis in aortic smooth muscle cells is achieved using mechanisms that are distinct from those operating in various acini and in striated muscles.
Centre de Biochimie, Centre National de la Recherche Scientifique, Nice, France.
P
P
Vigne
J P
JP
Breittmayer
M
M
Lazdunski
C
C
Frelin
D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D001839:Bombesin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D005434:Flow Cytometry; D007295:Inositol Phosphates / Q000096:biosynthesis; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D013268:Stimulation, Chemical; D014667:Vasopressins / Q000494:pharmacology*
D007295:Inositol Phosphates; D014667:Vasopressins; D001839:Bombesin; D002118:Calcium