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Pretreatment of pancreatic beta cells with pertussis toxin resulted in a 30% increase in peak whole-cell Ca2+ currents recorded in the absence of exogenous intracellular guanine nucleotides. Intracellular application of 90 microM GTP[gamma S], by liberation from a caged precursor, resulted in 40% reduction of the peak Ca2+ current irrespective of whether the current was carried by Ca2+ or Ba2+. Effects on the delayed outward K+ current were small and restricted to a transient Ca(2+)-dependent K+ current component. Inhibition by GTP[gamma S] of the Ca2+ current was not mimicked by standard GTP and could not be prevented either by pretreatment with pertussis toxin or by inclusion of GDP[beta S] or cyclic AMP in the intracellular medium. The inhibitory effect of GTP[gamma S] could be counteracted by a prepulse to a large depolarizing voltage. A similar effect of a depolarizing prepulse was observed in control cells with no exogenous guanine nucleotides. These observations indicate that inhibition of beta cell Ca2+ current by G protein activation results from direct interaction with the channel and does not involve second-messenger systems. Our findings also suggest that the beta cell Ca2+ current is subject to resting inhibition by G proteins.

Type

Journal article

Journal

Pflugers Arch

Publication Date

01/1992

Volume

420

Pages

72 - 77

Keywords

Animals, Calcium Channels, Electrophysiology, GTP-Binding Proteins, Guanosine 5'-O-(3-Thiotriphosphate), Guanosine Triphosphate, Intracellular Membranes, Islets of Langerhans, Mice, Pertussis Toxin, Potassium, Virulence Factors, Bordetella