Pflügers Archiv

, Volume 433, Issue 6, pp 679–690 | Cite as

A calcium-dependent chloride current in insulin-secreting βTC-3 cells

  • J. Ashot Kozak
  • D. E. Logothetis
ORIGINAL ARTICLE

Abstract

 Ca2+-dependent conductances have been hypothesized to play a role in the bursting pattern of electrical activity of insulin-secreting β cells in response to high plasma glucose. A Maxi K+ channel has received the most attention, while a low-conductance Ca2+-activated K+ current has also been identified. We used an increasingly popular β cell model system, the βTC-3 cell line, and the perforated-patch technique to describe the properties of a novel Ca2+-dependent Clcurrent [ICl(Ca)] in insulin-secreting pancreatic β cells. The reported ICl(Ca) could be activated under physiological Ca2+ concentrations and is the first of its kind to be described in pancreatic insulin-secreting cells. We found that long depolarizing steps above –20 mV elicited an outward current which showed slow inward relaxation upon repolarization to negative membrane potentials. Both the outward currents and the inward tails showed dependence on Ca2+ influx: their current/voltage (I/V) relations followed that of the ”L-like” Ca2+ current (ICa) present in these cells; they were blocked completely by the removal of external Ca2+ or application of Cd2+ at concentrations sufficient for complete block of ICa; and their magnitude increased with the depolarizing step duration. Moreover, the inward tail decayed monoexponentially with a time constant which at voltages negative to activation of ICa showed a weak linear voltage dependence, while at voltages positive to activation of ICa it followed the voltage dependence of ICa. This Ca2+-dependent current reversed at –21.5 mV and when the external Clconcentration was reduced from 159 mM to 62 mM the reversal potential shifted by ≈+20 mV as predicted by the Nernst relation for a Cl-selective current. Clchannel blockers such as DIDS (100 μM) and niflumic acid (100 μM) blocked this current. We concluded that this current was a Ca2+-dependent Clcurrent [ICl(Ca)]. From substitution of the external Clwith various monovalent anions and from the reversal potentials we obtained the following permeability sequence for ICl(Ca): I>NO3>Br>Cl>Acetate.

Key words Ca2+-activated Cl channel Perforated-patch recording Beta cell 

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Copyright information

© Springer-Verlag Berlin Heidelberg 1997

Authors and Affiliations

  • J. Ashot Kozak
    • 1
  • D. E. Logothetis
    • 1
  1. 1.Department of Physiology and Biophysics, Box 1218, Mount Sinai School of Medicine, C.U.N.Y., 1 Gustave L. Levy Place, New York, NY 10029-6574, USAUS

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