Interaction of atriopeptin III and vasopressin on calcium kinetics and contraction of aortic smooth muscle cells.

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Abstract
The cellular mechanism of the vasodilatory action of atriopeptin III (APIII) on vasopressin (AVP)-induced Ca2+ mobilization and cell shape change in cultured vascular smooth muscle cells (VSMC) was studied. APIII (10(-8) M) attenuated the increase of intracellular free Ca2+, [Ca2+]i, induced by 10(-8) M AVP (234.0 +/- 14.8 vs. 310.0 +/- 28.4 nM, P less than 0.01). Similar results were obtained in 45Ca2+ efflux experiments. APIII (10(-7) M), however, did not alter AVP-induced inositol trisphosphate (IP3) production, although the levels of inositol-1-phosphate were significantly reduced. The effect of APIII to block or attenuate AVP-induced Ca2+ mobilization was associated with an inhibition of AVP-stimulated cell shape change. The effect of atrial natriuretic factor (ANF) on cell shape, however, occurred at lower ANF concentrations than the effect on the Ca2+ mobilization. APIII stimulated production of cyclic guanosine monophosphate (cGMP) in VSMC. The effect of APIII on AVP-stimulated Ca2+ mobilization was partially mimicked by the stable nucleotide 8-bromo cGMP and was not affected by the soluble guanylate cyclase inhibitor, methylene blue (10(-4) M). These results suggest that APIII exerts its vasodilatory effect, in part, by interference with vasopressor-stimulated Ca2+ mobilization in vascular smooth muscle cells, perhaps by stimulating particulate guanylate cyclase and cGMP. However, an effect of ANF on the contractile mechanism at a site independent of Ca2+ release is also suggested by the present results.