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Am J Physiol Heart Circ Physiol 276: H651-H657, 1999;
0363-6135/99 $5.00
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Vol. 276, Issue 2, H651-H657, February 1999

Modulation of arterial Na+-K+-ATPase-induced [Ca2+]i reduction and relaxation by norepinephrine, ET-1, and PMA

Francisco Pérez-Vizcaíno, Angel Cogolludo, and Juan Tamargo

Departamento de Farmacología, Facultad de Medicina, Instituto de Farmacología y Toxicología, Universidad Complutense de Madrid, 28040 Madrid, Spain

Na+-K+-ATPase plays a major role in regulating membrane potential and vascular tone. We analyzed the modulation by norepinephrine (NE), endothelin-1 (ET-1), and phorbol 12-myristate 13-acetate (PMA) of Na+-K+-ATPase-induced cytoplasmic free Ca2+ concentration ([Ca2+]i) reduction and relaxation in isolated endothelium-denuded piglet mesenteric arteries. KCl (0.2-8.8 mM)-induced [Ca2+]i reduction and relaxation in arteries incubated in K+-free solution were used as functional indicators of Na+-K+-ATPase activity. KCl-induced relaxations after exposure to K+-free solution were associated with a reduction in [Ca2+]i, as measured by fura 2 fluorescence. However, KCl reduced [Ca2+]i below resting values, whereas force was reduced to near resting values. NE, ET-1, and PMA inhibited the relaxant effects of KCl, and this effect was attenuated by the protein kinase C inhibitor staurosporine but not by the phospholipase A2 inhibitor quinacrine. However, ET-1 and PMA potentiated the [Ca2+]i-reducing effect of KCl. In conclusion, ET-1, PMA, and NE are functional inhibitors of Na+-K+-ATPase activity in endothelium-denuded piglet mesenteric arteries, even when the direct effect on the enzyme activity may be stimulatory rather than inhibitory. This can be explained because ET-1, PMA, and NE induce Ca2+ sensitization for smooth muscle contraction, and therefore relaxations do not parallel the reductions in [Ca2+]i after the activation of Na+-K+-ATPase.

potassium chloride-induced relaxation; protein kinase C; fura 2 ; cytoplasmic free Ca2+ concentration; endothelin-1; phorbol 12-myristate 13-acetate


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