Lysophosphatidylcholine enhances I(Ks) currents in cardiac myocytes through activation of G protein, PKC and Rho signaling pathways

Lysophosphatidylcholine (LPC) is a bioactive phospholipid that accumulates rapidly in the ischemic myocardium. In recent years, it has been shown that some of the actions of LPC are mediated through the activation of the membrane G proteins. However, the precise mechanism(s) responsible for the LPC-related intracellular signaling in the regulation of cardiac ion channels are still poorly understood. The present study was undertaken to examine whether LPC regulates the slow component of the delayed rectifier K⁺ current (I_Ks) and, if so, what intracellular signals are important for this process. Isolated guinea pig cardiac myocytes were voltage-clamped using the whole-cell configuration of the patch-clamp method. The bath application of 1-palmitoyl-lysophosphatidylcholine (LPC-16) concentration-dependently (EC₅₀ = 0.7 μM) and reversibly increased I_Ks in atrial cells, but failed to potentiate I_Ks in ventricular myocytes. In contrast, 1-oleoyl-lysophosphatidylcholine (LPC-18:1) only produced a slight I_Ks increase, and 1-caproyl-lysophosphatidylcholine (LPC-6) or the LPC-16 precursor (phosphatidylcholine) had no effect on I_Ks. Pretreatment of atrial cells with an antibody against the N-terminus of the G2A receptor significantly reduced the LPC-16-induced potentiation of I_Ks. The inhibition of heterotrimeric G protein, phospholipase C (PLC) and protein kinase C (PKC) significantly reduced LPC-16-induced enhancement of I_Ks. Moreover, the blockade of Rho and Rho-kinase by specific inhibitors also inhibited the activity of LPC-16. Immunohistochemical studies demonstrated that G2A was densely distributed in the plasma membrane of atrial myocytes. Therefore, the present study suggests that the activation of a G protein (probably Gα_q) by LPC-16 potentiates I_Ks currents through the PLC-PKC and Rho-kinase pathways.