Recent evidence suggests that membrane potential can modulate the signaling pathways of GPCRs. Xenopus oocytes endogenously express a variety of GalphaqPCRs, including lysophosphatidic acid (LPA) receptors. We have shown that membrane voltage modulates InsP3-dependent Ca²⁺ release during LPA GPCR stimulation. The aim of this study was to further investigate this novel form of modulation and to elucidate the nature of the underlying voltage sensor.

Intracellular Ca²⁺ fluorescence (using fluo-5) and electrophysiological signals were recorded simultaneously. The plateau phase of the LPA-dependent Ca²⁺ mobilization was potentiated by depolarization and inhibited by hyperpolarization. In addition, the initial response to LPA was modulated by the holding potential being greater at -80 mV than at ­20 mV both the latency of LPA (10nM)-evoked Ca²⁺ increase (42±4 s vs. 16±1 s, p<0.05) and the time to peak (65±6 s vs. 43±1 s, p<0.05). The peak response to LPA was also affected by the holding potential, being larger at ­20 mV than at ­80 mV (178±7 f/f0 vs. 131±10 f/f0, p<0.05). Membrane depolarization enhanced LPA receptor-evoked Ca²⁺ mobilization over a wide range of agonist concentrations. Voltage-dependent Ca²⁺ release was not observed following direct elevation of InsP3 or after activation of G-proteins in the absence of agonist, indicating that the primary site of action of membrane voltage is the receptor itself. This novel modulation of LPA signaling by membrane potential may have important consequences for control of Ca²⁺ signals in a variety of tissues.

Supported by GV06/323 and BFU2006-04781.