Increasing intracellular calcium of guinea pig ventricular myocytes induced by platelet activating factor through IP3 pathway

We used Fluo-3/AM to examine the effect of platelet-activating factor on the intracellular Ca2+ ([Ca2+](i)) levels in isolated myocytes of guinea pig ventricle. Myocytes were isolated with Langendorff perfusion technique and were challenged with platelet-activating factor. Addition of platelet-activating factor (1 pM to 10 nM) significantly increased the [Ca2+](i) in the presence and absence of extracellular Ca2+. The notion that increases in intracellular Ca2+ induced by platelet-activating factor is the result of stimulation of intracellular Ca2+ pool rather than increasing Ca2+ influx was further supported by the whole cell patch-clamp experiments in which the platelet-activating factor did not alter the activity of L-type of Ca2+ channels (ICa-L). Treatment of myocytes with ryanodine failed to abolish the stimulatory effect of platelet-activating factor on [Ca2+](i). In contrast, inhibition of IP3-sensitive Ca2+ release pool with 2-aminoethoxydiphenyl borate (2-APB) blocked the effect of platelet-activating factor. We conclude that the platelet-activating factor-induced increase in intracellular Ca2+ is mediated by stimulation of IP3 receptor but not by stimulation of ICa-L and ryanodine-sensitive receptor.