Single-channel activities of the human epithelial Ca2+ transport proteins CaT1 and CaT2.
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 microm) 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.
Vassilev
P M
PM
Endocrine-Hypertension, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 221 Longwood Ave., Boston, MA 02115, USA.
Peng
J B
JB
Hediger
M A
MA
Brown
E M
EM
D026923:Amino Acid Transport Systems, Basic; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D004847:Epithelial Cells / Q000502:physiology; D006801:Humans; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D009865:Oocytes / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D018075:RNA, Complementary / Q000235:genetics; D051381:Rats; D012964:Sodium / Q000378:metabolism; D050916:TRPV Cation Channels; D014162:Transfection; D014982:Xenopus laevis
D026923:Amino Acid Transport Systems, Basic; D015220:Calcium Channels; D018075:RNA, Complementary; C414177:SLC7A2 protein, human; D050916:TRPV Cation Channels; C120776:TRPV6 channel; D012964:Sodium; D008274:Magnesium; D011188:Potassium; D002118:Calcium