G-PROTEIN ACTIVATION, INTRACELLULAR CA2- IN XENOPUS OOCYTES( MOBILIZATION AND PHOSPHORYLATION STUDIES OF MEMBRANE CURRENTS INDUCED BY ALF4)

We have examined the electrophysiological responses induced by alumini um fluoride (AlF4-) and carbachol in Xenopus oocytes. Application of A lF4- induced Ca2+-dependent oscillatory and smooth Cl- currents. Pre-t reatment of oocytes with microinjected guanosine 5'-O-(2-thiodiphospha te) diminished the currents, indicating that. the effect of AlF4- occu rred through G-protein activation. Confocal imaging of intracellular C a2+ clearly demonstrated that AlF4- could increase the internal Ca2+ c oncentration in oocytes in the absence of external Ca2+. A protein kin ase (PK) activator (4-beta-phorbol 12,13-dibutyrate) decreased the AlF 4-;-induced membrane currents, whereas a PK inhibitor (staurosporine) caused an increase. On the other hand, the protein phosphatase inhibit or (okadic acid) showed little effect. Although the effects of the pho sphorylating/dephosphorylating agents on the carbachol-induced current s were qualitatively similar to the case of AlF4- some quantitative di fference was noted. The results are discussed in terms of the signalin g pathways involving muscarinic receptors and G-protein(s) in Xenopus oocytes.