Activation of G-proteins induces Ca2+ oscillations with hyperpolarizing K+ currents in pancreatic beta-cells.
Activation of G-proteins by internal perfusion with GTP-gamma-S or external application of carbachol resulted in oscillations of cytoplasmic Ca2+ in isolated mouse pancreatic beta-cells. The Ca2+ transients were associated with the generation of K+ currents sufficiently pronounced to induce marked pulses of hyperpolarization. The oscillatory G-protein response remained largely unaffected when altering the membrane potential. The oscillations became less frequent in the presence of 1 mM neomycin and disappeared when the cells were internally perfused with 100 micrograms/ml heparin. The frequency of the oscillations was positively correlated with the basal level of cytoplasmic Ca2+. Addition of Ca2+ to the internal perfusion medium increased the oscillatory rate and buffering of the ion with Indo-1 or EGTA had the opposite effect. It is concluded that G-protein activation results in cyclic mobilisation of intracellular calcium mediated by inositol-1,4,5-triphosphate and that the basal concentration of cytoplasmic Ca2+ is an important determinant for the frequency of the oscillations.
Department of Medical Cell Biology, Uppsala University, Sweden.
P E
PE
Lund
B
B
Hellman
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008820:Mice, Obese; D009355:Neomycin / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*
D016244:Guanosine 5'-O-(3-Thiotriphosphate); D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D019204:GTP-Binding Proteins; D009355:Neomycin; D011188:Potassium; D002118:Calcium