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 Ca 2+ ([Ca 2+ ] 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 (I pM to 10 nM) significantly increased the [Ca 2+ ] i in the presence and absence of extracellular Ca 2+ . The notion that increases in intracellular Ca 2+ induced by platelet-activating factor is the result of stimulation of intracellular Ca 2+ pool rather than increasing Ca 2+ 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 Ca 2+ channels (I Ca-L ). Treatment of myocytes with ryanodine failed to abolish the stimulatory effect of platelet-activating factor on [Ca 2+ ] i . In contrast, inhibition of IP 3 -sensitive Ca 2+ 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 Ca 2+ is mediated by stimulation of IP 3 receptor but not by stimulation of I Ca-L and ryanodine-sensitive receptor.