Voltage-activated Na+ currents and their suppression by phorbol ester in clonal insulin-producing RINm5F cells

P. Rorsman, P. Arkhammar, P. O. Berggren

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34 Scopus citations


The whole-cell configuration of the patch-clamp technique was applied on the clonal insulin-producing cell line RINm5F. Thus attempts were made to characterize voltage-activated inward and outward membrane currents and to examine to what extent these were affected by both long-term and acute exposure to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). Current responses to voltage-clamp steps up to -40 mV were small. A pulse to -28 mV evoked an inward current, and slowly activating outward currents developed at potentials above -20 mV. The inward current had a V-shaped current-voltage relationship, reaching a peak between -10 and 0 mV, whereas the outward current increased linearly at potentials beyond -20 mV. It was demonstrated that the inward currents are carried primarily by Ca2+ and Na+ and the outward current by K+. After long-term exposure to TPA, there was a suppression of Na+ current in one-third of the cells, whereas the Ca2+ and K+ currents were unaffected. Acute exposure to the phorbol ester increased the Ca2+ currents with little effect on the Na+ currents. The extent to which the differences in effects on membrane currents initiated by respective acute and long-term exposure to TPA may reflect two separate mechanisms of protein kinase C activation, the latter related to regulation of differentiation of the RINm5F cells, merits further investigation.

Original languageEnglish (US)
Pages (from-to)C912-C919
JournalAmerican Journal of Physiology - Cell Physiology
Issue number6 (20/6)
StatePublished - 1986

ASJC Scopus subject areas

  • Physiology
  • Cell Biology


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