title: Early agonist-mediated ionic events in cultured vascular smooth muscle cells. Calcium mobilization is associated with intracellular acidification.
abstract: Angiotensin II, a potent vasoconstrictor peptide, increases free cytoplasmic Ca2+ concentration ([Ca2+]i) in vascular smooth muscle cells (VSMC) by release of nonmitochondrial Ca2+ stores and stimulates an amiloride-sensitive Na+ influx, presumably via Na+/H+ exchange. We recently have found that the angiotensin II-mediated change in VSMC intracellular pH has two components, an early rapid acidification phase and a slower recovery phase involving Na+-dependent alkalinization. In the present study, we show that the early acidification is not mediated via Na+/H+ exchange. Instead, we propose a mechanism which involves increases in [Ca2+]i and Ca2+ efflux with a subsequent rise in intracellular H+. Agonists, in addition to angiotensin II, which increase [Ca2+]i in cultured VSMC, including platelet-derived growth factor, vasopressin, and bradykinin, induce an acidification, while agonists which fail to raise [Ca2+]i do not. The time course and magnitude of agonist-stimulated 45Ca2+ efflux correlate with the acidification response. The angiotensin II concentration-response relationship for acidification and Ca2+ mobilization are similar. Furthermore, inhibition of changes in [Ca2+]i by treatment with phorbol ester, cyclic GMP, or quin2 loading prevent agonist-mediated acidification. The effects of altering extracellular [Ca2+] and [H+] on agonist-mediated intracellular acidification and H+ efflux suggest that the acidification is due to ATP-dependent unidirectional H+ influx, perhaps via the plasma membrane Ca2+-ATPase, and not to a Ca2+/H+ antiport. This agonist-mediated acidification represents a previously undescribed ionic event in VSMC activation which may be involved in excitation-response coupling.
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000634:Aminoquinolines / Q000378:metabolism; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D006152:Cyclic GMP / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D000634:Aminoquinolines; D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D000804:Angiotensin II; D000584:Amiloride; D012964:Sodium; D000252:Calcium-Transporting ATPases; D006152:Cyclic GMP; D013755:Tetradecanoylphorbol Acetate; C035739:Quin2; D002118:Calcium