Interactions of saponin with microsomal membranes isolated from vascular smooth muscle.

The effects of the plant glycosides extract, saponin, on various biochemical properties of microsomal fractions isolated from dog aortae and mesenteric arteries were investigated. These properties include binding and transport of Ca2+, ouabain-sensitive K+ activated p-nitrophenyl phosphatase (hereafter termed K+-pNPPase) and binding of radiolabelled antagonists to adrenoceptors. We found that saponin inhibited both Ca2+ binding and transport by the vascular muscle microsomes in a dose-dependent manner, but it caused marked enhancement of the K+-pNPPase activity.

Beta adrenoreceptor in vascular smooth muscle with special reference to subcellular localization and number of binding sites.

The binding of monoiodinated cyanopindolol (ICYP) to membranes from canine and rat aortas, mesenteric arteries and mesenteric nerves has been studied. Binding of ICYP was shown by differential centrifugation and sucrose gradient purification as well as digitonin treatment to be directly related to the content of arterial muscle plasma membrane assessed by marker enzymes. The Kd values obtained were all in the range of 10 to 30 pM but maximum binding site (Bmax) values varied depending upon the extent of contamination by nonplasmalemmal membranes.