Permeation of divalent cations through the Ca2+ channel of rabbit portal vein myocytes.
The divalent selectivity of the Ca2+ channel in the rabbit portal vein myocyte was examined by the whole cell clamp method. A concentration-dependent selectivity of divalent ion permeation was found such that when Ca2+ was replaced by Ba2+ or Sr2+, the order of maximum current was Ca2+ = Ba2+ greater than Sr2+ at 2 mM and Ba2+ greater than Sr2+ greater than or equal to Ca2+ at 5-10 mM. The possibility of block of the Ca2+ channel by micromolar concentrations of "contaminant" Ca2+ as a determinant of change in the order of selectivity of divalents was examined. Ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (500 microM) significantly increased maximum Ba2+ current (IBa) or ISr in solution containing 5 mM Ba2+ or Sr2+. Furthermore, at 5 mM extracellular Ba2+ concentration, addition of 10, 20, 50, and 100 microM Ca2+ caused a 6, 14, 22, and 33% decrease in IBa, respectively. These results suggest that the portal vein Ca2+ channel has three orders of magnitude higher selectivity for Ca2+ over Ba2+ and Sr2+ such that micromolar Ca2+ may block permeation of other divalents through the channel.
Katzka
D A
DA
Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104.
Cox
R
R
Davidoff
A J
AJ
Morad
M
M
D000818:Animals; D001464:Barium / Q000493:pharmacokinetics; D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D002413:Cations, Divalent / Q000493:pharmacokinetics*; D002463:Cell Membrane Permeability; D002469:Cell Separation; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D011169:Portal Vein / Q000166:cytology / Q000378:metabolism*; D011817:Rabbits
D015220:Calcium Channels; D002413:Cations, Divalent; D001464:Barium; D002118:Calcium