CELL MEMBRANE POTENTIAL AND INSULIN RELEASE; ROLE OF CALCIUM AND CALCIUM: MAGNESIUM RATIO

¹ Department of Biophysics, School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, U.K.
² Department of Histology and Cell Biology, University of Umeå, S-901 87, Umeå, Sweden
³ Department of Neurosciences, Centro de Investigación y Estudios Avanzados del IPN, México, D.F.
⁴ Metabolic Research Unit and Department of Biochemistry & Biophysics, University of California, San Francisco, CA 94143, U.S.A.

Glucose-induced insulin release from perfused rat pancreas was compared with glucose-induced changes in membrane potential of cells from mouse islets. Extracellular concentrations of Ca and Mg were varied as steps, simultaneously or separately, from 10% to 200% of normal in the presence of 11·1 mM glucose. A change in Ca induced a transient change in electrical activity paralleled by a transient change in insulin release. If the Ca/Mg ratio was maintained, steady-state insulin release remained constant between 10% and 200% Ca, while electrical activity showed alterations. Analysis of burst parameters indicated that increased or decreased Ca entry was balanced by decreased or increased excitability. It is postulated that the cell contains a compensator mechanism for the regulation of Ca influx.