Phosphatidic acid increases inositol-1,4,5,-trisphosphate and [Ca2+]i levels in neonatal rat cardiomyocytes.
Phosphatidic acid (PA), which can be synthesized de novo, or as a product of phosphatidylcholine hydrolysis and/or phosphorylation of 1,2-diacylglycerol (DAG), mediates diverse cellular functions in various cell types, including cardiomyocytes. We set out to characterize the effect of PA on intracellular free calcium ([Ca2+]i) and inositol-1,4,5-trisphosphate (IP(3)) levels in primary cultures of neonatal rat cardiomyocytes. Addition of PA led to rapid, concentration and time dependent increases in both IP(3) and [Ca2+]i levels in adherent cells. There was strong correlation in the concentration-response relationships between IP(3) and [Ca2+]i increases evoked by PA. Incubation with the sarcoplasmic reticulum (SR) Ca2+ pump inhibitor, cyclopiazonic acid (CPA), significantly attenuated the PA evoked [Ca2+]i increase but had no significant effect on IP(3) accumulation. The phospholipase C (PLC) inhibitor, D-609, attenuated both IP(3) and [Ca2+]i elevations evoked by PA whereas staurosporine (STS), a potent and non-selective PKC inhibitor, had no significant effect on either. Another PLC inhibitor, U73122, but not its inactive analog, U73343, also inhibited PA evoked increases in [Ca2+]i. Depletion of extracellular calcium attenuated both basal and PA evoked increases in [Ca2+]i. The PLA(2) inhibitors, bromophenylacyl-bromide (BPB) and CDP-choline, had no effect on PA evoked [Ca2+]i responses. Neither the DAG analog, dioctanoylglycerol, nor the DAG kinase inhibitor, R59949, affected PA evoked changes in [Ca2+]i. Taken together, these data indicate that PA, in a manner independent of PKC, DAG, or PLA(2), may enhance Ca2+ release from IP(3) sensitive SR Ca(2+) stores via activation of PLC in neonatal rat cardiomyocytes.
Liu
P
P
Cardiovascular Risk Factor Reduction Unit (CRFRU), Department of Pharmacology, College of Medicine, University of Saskatchewan, 107 Wiggins Rd, Saskatoon, Saskatchewan, Canada.
Xu
Y
Y
Hopfner
R L
RL
Gopalakrishnan
V
V
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis / Q000378:metabolism*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010712:Phosphatidic Acids / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D010712:Phosphatidic Acids; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium