Permeation of divalent cations through the Ca2+ channel of rabbit portal vein myocytes

Am J Physiol. 1992 Feb;262(2 Pt 2):H326-30. doi: 10.1152/ajpheart.1992.262.2.H326.

Abstract

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Barium / pharmacokinetics
  • Calcium / pharmacology
  • Calcium Channels / metabolism*
  • Cations, Divalent / pharmacokinetics*
  • Cell Membrane Permeability
  • Cell Separation
  • Muscle, Smooth, Vascular / cytology
  • Muscle, Smooth, Vascular / metabolism*
  • Osmolar Concentration
  • Portal Vein / cytology
  • Portal Vein / metabolism*
  • Rabbits

Substances

  • Calcium Channels
  • Cations, Divalent
  • Barium
  • Calcium