Mechanisms of lysophosphatidic acid-induced increase in intracellular calcium in vascular smooth muscle cells

Abstract

Although lysophosphatidic acid (LPA) is known to cause an increase in intracellular Ca 2+ concentration ([Ca 2+] i ) in vascular smooth muscle cells (VSMCs), the mechanisms of [Ca 2+] i mobilization by LPA are not fully understood. In the present study, the effect of LPA on [Ca 2+] i mobilization in cultured A10 VSMCs was examined by Fura-2 fluorescence technique. The expression of LPA receptors was studied by immunostaining. LPA was observed to increase [Ca 2+] i in a concentration-dependent manner; this increase was dependent on the concentration of extracellular Ca 2+. Both sarcolemmal (SL) Na +–Ca 2+ exchange inhibitors (amiloride, Ni 2+ and KB-R7943) and Na +–H + exchange inhibitor (MIA) as well as SL store-operated Ca 2+ channel (SOC) antagonists (SK&F 96365, tyrphostin A9 and gadolinium), unlike SL Ca 2+ channel antagonists (verapamil and diltiazem), inhibited the LPA-induced increase in [Ca 2+] i . In addition, sarcoplasmic reticulum (SR) Ca 2+ channel blocker (ryanodine), SR Ca 2+ channel opener (caffeine), SR Ca 2+ pump ATPase inhibitor (thapsigargin) and inositol 1,4,5-trisphosphate (InsP 3) receptor antagonists (xestospongin and 2-aminoethoxydiphenyl borate) were found to inhibit the LPA-induced Ca 2+ mobilization. Furthermore, phospholipase C (PLC) inhibitor (U 73122) and protein kinase C (PKC) activator (phorbol 12-myristate 13-acetate) attenuated the LPA-induced increase in [Ca 2+] i . These results indicate that Ca 2+ mobilization by LPA involves extracellular Ca 2+ entry through SL Na +–Ca 2+ exchanger, Na +–H + exchanger and SL SOCs. In addition, ryanodine-sensitive and InsP 3-sensitive intracellular Ca 2+ pools may be associated with the LPA-induced increase in [Ca 2+] i . Furthermore, the LPA-induced [Ca 2+] i mobilization in VSMCs seems to be due to the activation of both PLC and PKC.