DIRECT STIMULATION OF PHOSPHATIDYLINOSITOL DEGRADATION BY ADDITION OF VASOPRESSIN TO PURIFIED RAT LIVER PLASMA MEMBRANES

Abstract

Rat liver plasma membranes were incubated in Ca²⁺ -free buffer plus 0.5 mM ethyleneglycol-bis (betaaminoethyl ether)-N, N¹-tetraacetic acid (ECTA) containing 0.5 mg/ml deoxycholate or 50 mU/ml vasopressin or both compounds. The membrane phospholipids were extracted, separated by two-dimensional chromatography and quantitated by phosphorus analysis. Vasopressin significantly enhanced degradation of phosphatidylinositol in the presence of deoxycholate (21% with deoxycholate alone versus 32% in the presence of vasopressin plus deoxycholate). However, no significant effects of deoxycholate or vasopressin were seen on the degradation of phosphatidylcholine, phosphatidylethanolamine or phosphatidylserine. These results indicate that specific degradation of phosphatidylinositol can be seen after direct addition of vasopressin to a plasma membrane preparation.