SELECTIVE ACTIVATION BY ATRIAL-NATRIURETIC-FACTOR OF PHOSPHATIDYLCHOLINE-SPECIFIC PHOSPHOLIPASE ACTIVITIES IN PURIFIED HEART-MUSCLE PLASMA-MEMBRANES

We have characterized a membrane-bound phosphatidylcholine (PC) specif ic phospholipase C (PC-PLC) in plasma membranes from rat cardiac muscl e, and have investigated the role of PC-PLC and PG-specific phospholip ase D (PC-PLD) activities in the mechanism of action of atrial natriur etic factor (ANF). In purified sarcolemma, ANF stimulated over a wide range of concentrations with a maximum at 10(-11) M the hydrolysis of phosphatidylcholine through PC-PLD giving phosphatidate and choline, w hereas higher concentrations of ANF (10(-10) M) preferentially stimula ted PC breakdown through PC-PLC to form diacylglycerol and phosphochol ine. To confirm the involvement of the PC-PLD in the mechanism of ANF action, we measured the transphosphatidylation reaction, a specific as say for this phospholipase which in the presence of ethanol catalyses the phosphatidylethanol formation from PC. ANF stimulated phosphatidyl ethanol formation with the same dose-response behavior as phosphatidat e formation. The significant diacylglycerol increase at 10(-10) M ANE: in the presence of propranolol, a potent inhibitor of phosphatidate p hosphatase which can hydrolyse phosphatidate to give diacylglycerol, s uggested a direct involvement of PC-PLC. The use of GTP-gamma-S, a non hydrolysable analog of GTP, and of pertussis toxin showed the involve ment of a pertussis toxin insensitive G protein in PC-PLC mediated ANF signal transduction. We suggest a differential effect of ANF on PC br eakdown by phospholipases C and D depending on the concentration of th e peptide.