Mechanisms of the lysophosphatidic acid‐induced increase in [Ca2+]iin skeletal muscle cells

AbstractAlthough lysophosphatidic acid (LPA) is known to increase intracellularfree calcium concentration ([Ca2+]i) in different cell types, the effect of LPA on the skeletal muscle cells is not known. The present study was therefore undertaken to examine the effect of LPA on the [Ca2+]iin C2C12 cells. LPA induced a concentration and time dependent increase in [Ca2+]i, which was inhibited by VPC12249, VPC 32183 and dioctanoyl glycerol pyrophosphate, LPA1/3 receptor antagonists. Pertussis toxin, a Giprotein inhibitor, also inhibited the LPA‐induced increase in [Ca2+]i. Inhibition of tyrosine kinase activities with tyrphostin A9 and genistein also prevented the increase in [Ca2+]idue to LPA. Likewise, wortmannin and LY 294002, phosphatidylinositol 3‐kinase (PI3‐K) inhibitors, inhibited [Ca2+]iresponse to LPA. The LPA effect was also attenuated by ethylene glycolbis(β‐aminoethylether)‐N,N,N′,N′‐tetraacetic acid (EGTA), an extracellular Ca2+chelator, Ni2+and KB‐R7943, inhibitors of the Na+‐Ca2+exchanger; the receptor operated Ca2+channel (ROC) blockers, 2‐aminoethoxydiphenyl borate and SK&F 96365. However, the L‐type Ca2+channel blockers, verapamil and diltiazem; the store operated Ca2+channel blockers, La3+and Gd3+; a sarcoplasmic reticulum calcium pump inhibitor, thapsigargin; an inositol trisphosphate receptor antagonist, xestospongin and a phospholipase C inhibitor, U73122, did not prevent the increase [Ca2+]idue to LPA. Our data suggest that the LPA‐induced increase in [Ca2+]imight occur through Gi‐protein coupled LPA1/3receptors that may be linked to tyrosine kinase and PI3‐K, and may also involve the Na+‐Ca2+exchanger as well as the ROC. In addition, LPA stimulated C2C12 cell proliferationviaPI3‐K. Thus, LPA may be an important phospholipid in the regulation of [Ca2+]iand growth of skeletal muscle cells.