Single-channel activities of the human epithelial Ca2+ transport proteins CaT1 and CaT2.
J Membr Biol
; 184(2): 113-20, 2001 Nov 15.
Article
de En
| MEDLINE
| ID: mdl-11719848
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 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.
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Collection:
01-internacional
Base de données:
MEDLINE
Sujet principal:
Canaux calciques
/
Calcium
Limites:
Animals
/
Humans
Langue:
En
Journal:
J Membr Biol
Année:
2001
Type de document:
Article
Pays d'affiliation:
États-Unis d'Amérique