Calcium-activated phospholipase C associated with canine renal basolateral membranes

To determine whether calcium-activated phospholipase C effects breakdown of phospholipids present in the basolateral membrane of the renal proximal tubular cell we incubated proximal tubular basolateral membranes isolated from dog kidney in the absence and presence of deoxycholate, and varied free calcium from 0 to 300 microM. Following incubations, lipids were extracted from membranes and separated using thin-layer chromatography. In the absence of deoxycholate, neither phosphatidylinositol nor diglyceride extractable from basolateral membranes changed significantly as calcium was increased. In the presence of deoxycholate, extractable phosphatidylinositol and diglyceride did not change significantly as free calcium was elevated from 0 to 0.03 microM, but phosphatidylinositol decreased and diglyceride increased progressively as 0.03-300 microM free calcium was included in incubations. Most of the increased extractable diglyceride could be accounted for by hydrolysis of phosphatidylinositol as reflected by decreased extractable phosphatidylinositol. Our findings suggest that calcium-activated phospholipase C effects breakdown of phospholipids present in the basolateral portion of the plasma membrane of the renal proximal tubular cell. It is possible that this enzyme plays a role in stimulating protein kinase c at this site.