Single-Channel Activities of the Human Epithelial Ca2+ Transport Proteins CaT1 and CaT2 |
| |
Authors: | P.M. Vassilev J.-B. Peng M.A. Hediger E.M. Brown |
| |
Affiliation: | (1) Endocrine-Hypertension, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 221 Longwood Ave., Boston, MA 02115, USA, US;(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, USA, US |
| |
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. Received: 8 March 2001/Revised: 24 July 2001 |
| |
Keywords: | : Calcium — Single channels — Voltage-dependence — Hyperpolarization-activated currents |
本文献已被 SpringerLink 等数据库收录! |
|