The Journal of Membrane Biology

, Volume 184, Issue 2, pp 113-120

First online:

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

  • P.M.  VassilevAffiliated withEndocrine-Hypertension, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 221 Longwood Ave., Boston, MA 02115, USA
  • , J.-B.  PengAffiliated withRenal Divisions and Membrane Biology Program, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 221 Longwood Ave., Boston, MA 02115, USA
  • , M.A.  HedigerAffiliated withRenal Divisions and Membrane Biology Program, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 221 Longwood Ave., Boston, MA 02115, USA
  • , E.M.  BrownAffiliated withEndocrine-Hypertension, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 221 Longwood Ave., Boston, MA 02115, USA

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access

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