Liu P, Xu Y, Hopfner R L, Gopalakrishnan V
Cardiovascular Risk Factor Reduction Unit (CRFRU), Department of Pharmacology, College of Medicine, University of Saskatchewan, 107 Wiggins Rd, Saskatoon, Saskatchewan, Canada.
Biochim Biophys Acta. 1999 Aug 25;1440(1):89-99. doi: 10.1016/s1388-1981(99)00115-8.
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.
磷脂酸（PA）可从头合成，也可作为磷脂酰胆碱水解和/或1,2 - 二酰甘油（DAG）磷酸化的产物，在包括心肌细胞在内的各种细胞类型中介导多种细胞功能。我们着手研究PA对新生大鼠心肌细胞原代培养物中细胞内游离钙（[Ca2+]i）和肌醇 - 1,4,5 - 三磷酸（IP(3)）水平的影响。添加PA导致贴壁细胞中IP(3)和[Ca2+]i水平迅速、浓度和时间依赖性增加。PA引起的IP(3)和[Ca2+]i增加之间的浓度 - 反应关系存在很强的相关性。与肌浆网（SR）Ca2+泵抑制剂环匹阿尼酸（CPA）孵育可显著减弱PA引起的[Ca2+]i增加，但对IP(3)积累无显著影响。磷脂酶C（PLC）抑制剂D - 609减弱了PA引起的IP(3)和[Ca2+]i升高，而强效非选择性蛋白激酶C（PKC）抑制剂星形孢菌素（STS）对两者均无显著影响。另一种PLC抑制剂U73122，但不是其无活性类似物U73343，也抑制了PA引起的[Ca2+]i增加。细胞外钙耗竭减弱了基础和PA引起的[Ca2+]i增加。磷脂酶A(2)抑制剂溴苯酰溴（BPB）和胞苷二磷酸胆碱对PA引起的[Ca2+]i反应无影响。二辛酰甘油（DAG类似物）和DAG激酶抑制剂R59949均未影响PA引起的[Ca2+]i变化。综上所述，这些数据表明，PA可能通过激活新生大鼠心肌细胞中的PLC，以独立于PKC、DAG或磷脂酶A(2)的方式增强IP(3)敏感的SR Ca(2+)储存中的Ca2+释放。
