Atriopeptin II and 8-bromo-cGMP lower Ca/sup 2 +/ in cultured aortic smooth muscle cells
Atriopeptin II and 8-bromo-cGMP lower Ca/sup 2 +/ in cultured aortic smooth muscle cells Atriopeptin II (ANP) or 8-Bromo-cGMP (8-Br-cGMP) decreased the levels of intracellular Ca/sup 2 +/ in Angiotensin II- (Ang) or K/sup +/-stimulated cultured rat aortic smooth muscle cells. Cytoplasmic Ca/sup 2 +/, measured by fura-2 fluorescence, was maximal at 30 to 60 sec following the addition of either Ang or KCl. Pretreatment of smooth muscle cells with ANP or 8-Br-cGMP diminished peak levels of Ca/sup 2 +/ in response to Ang or KCl. Because the source of Ca/sup 2 +/ mobilized by KCl was extracellular while that mobilized by Ang was intracellular, these results suggested that ANP and 8-Br-cGMP did not inhibit the mobilization of Ca/sup 2 +/. This was further supported by studies on the effects of ANP and 8-Br-cGMP on inositol polyphosphate production in cells labelled with /sup 3/H-inositol. Ang, but not KCl, produced time-dependent increases in inositol polyphosphates. On the other hand, they have observed that cGMP-dependent protein kinase (cGPK), but not cAMP-dependent protein kinase, caused a 4-fold stimulation of Ca/sup 2 +/ ATPase activity in crude microsomal fractions from cultured rat aortic smooth muscle cells. These results suggest that ANP and 8-Br-cGMP may lower Ca/sup 2 +/ mobilized by Ang or KCl by enhancing Ca/sup 2 +/ more »
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