G-protein activation, intracellular ca²⁺ mobilization and phosphorylation studies of membrane currents induced by A1F₄^- in xenopus oocytes

We have examined the electrophysiological responses induced by aluminium fluoride (AlF₄^-) and carbachol in Xenopus oocytes. Application of AlF₄^- induced Ca²⁺-dependent oscillatory and smooth C1^- currents. Pre-treatment of oocytes with microinjected guanosine 5'-0 (2-thiodiphosphate) diminished the currents, indicating that the effect of AlF₄^- occurred through G-protein activation. Confocal imaging of intracellular Ca²⁺ clearly demonstrated that AlF₄^- could increase the internal Ca²⁺ concentration in oocytes in the absence of external Ca²⁺. A protein kinase (PK) activator (4-β-phorbol 12,13-dibutyrate) decreased the AlF₄^- induced membrane currents, whereas a PK inhibitor (staurosporine) caused an increase. On the other hand, the protein phosphatase inhibitor (okadaic acid) showed little effect. Although the effects of the phosphorylating/dephosphorylating agents on the carbachol-induced currents were qualitatively similar to the case of AlF₄^-, some quantitative difference was noted. The results are discussed in terms of the signaling pathways involving muscarinic receptors and G-protein(s) in Xenopus oocytes.