Lysophosphatidic acid potentiates ACh receptor currents by G-protein-mediated activation of protein kinase C.

The effect of lysophosphatidic acid (lysoPA) on acetylcholine (ACh)-evoked currents was examined using normal and mutant Torpedo nicotinic ACh receptors expressed in Xenopus oocytes. LysoPA enhanced ACh-evoked currents in a washing time- and dose-dependent manner at concentrations of 0.1-3 microM, reaching a maximum of 210% 30 min after treatment, and instead, higher concentrations of lysoPA potentiated to a lesser extent or inhibited the currents. Dose-response curve to ACh was not affected by treatment with lysoPA. Current potentiation by lysoPA was fully inhibited by a broad G-protein inhibitor, guanosine-5'-O-(2-thiodiphosphate) (GDPbetaS), but not by a Gi/o-protein inhibitor, pertussis toxin (PTX). Additionally, the selective protein kinase C (PKC) inhibitor, GF109203X, blocked the potentiation, although the effect of lysoPA was not affected by the selective cAMP-dependent protein kinase (PKA) inhibitor, H-89, or mitogen-activated protein kinase inhibitor, PD98059. LysoPA (3 microM) enhanced currents to 130% in Ca2+-free extracellular solution, and to 150% still in the mutant ACh receptors lacking PKC phosphorylation sites. The potentiation was also completely blocked by GF109203X. These results indicate that lysoPA potentiates ACh receptor currents by PTX-insensitive G-protein-mediated activation of Ca2+-dependent/-independent PKCs with subsequent phosphorylation of the receptors and by an unknown factor or process activated by PKC activation.