The Journal of Membrane Biology

, Volume 184, Issue 2, pp 113–120

Single-Channel Activities of the Human Epithelial Ca2+ Transport Proteins CaT1 and CaT2

  • P.M.  Vassilev
  • J.-B.  Peng
  • M.A.  Hediger
  • E.M.  Brown

Abstract.

The human epithelial channels, CaT1 and CaT2, were expressed in oocytes, and their single-channel characteristics were compared. In the presence of Na+ and K+ as charge carriers in the pipette solutions, channel activities were observed only when the the extracellular sides of the patches were exposed to nominally Ca2+- and Mg2+-free solutions. In patches of both CaT1- and CaT2-expressing oocytes, multiple channel openings were observed, but the current levels were higher in CaT2-expressing oocytes, particularly at more negative voltages. With K+ as a charge carrier in patches of CaT1-expressing oocytes, the channel activity was low at −10 to −60 mV, but increased dramatically at more negative potentials. This voltage dependence was observed in the presence of both Na+ and K+. The channel activity with Na+, however, was higher at all potentials. Differences between the voltage dependencies for the two cations were also observed in CaT2-expressing oocytes, but the channel activities were higher than those in CaT1-expressing oocytes, particularly in the presence of Na+. We also found that low concentrations of extracellular Mg2+ (5–50 μm) elicited a strong inhibitory action on the CaT channels. Activation of the CaT1 and CaT2 channels by hyperpolarization and other factors may promote increased Ca2+ entry that participates in stimulation of intestinal absorption and renal reabsorption and/or other Ca2+ transport mechanisms in epithelial cells.

Key words: Calcium — Single channels — Voltage-dependence — Hyperpolarization-activated currents 

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Copyright information

© 2001 Springer-Verlag New York Inc.

Authors and Affiliations

  • P.M.  Vassilev
    • 1
  • J.-B.  Peng
    • 2
  • M.A.  Hediger
    • 2
  • E.M.  Brown
    • 1
  1. 1.Endocrine-Hypertension, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 221 Longwood Ave., Boston, MA 02115, USAUS
  2. 2.Renal Divisions and Membrane Biology Program, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 221 Longwood Ave., Boston, MA 02115, USAUS

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