Whole-cell and Single Channel Monovalent Cation Currents Through the Novel Rabbit Epithelial Ca2+ Channel ECaC

J Physiol. 2000 Sep 1;527 Pt 2(Pt 2):239-48. doi: 10.1111/j.1469-7793.2000.00239.x.

Abstract

This study describes properties of monovalent cation currents through ECaC, a recently cloned epithelial Ca2+-permeable channel from rabbit. The kinetics of currents through ECaC was strongly modulated by divalent cations. Currents were inhibited in the presence of extracellular Ca2+. They showed an initial voltage-dependent decay in the presence of mM Mg2+ at hyperpolarizing steps in Ca2+-free solutions, which represents a voltage-dependent Mg2+ block through binding of Mg2+ to a site localized in the electrical field of the membrane (delta = 0.31) and a voltage-dependent binding constant (at 0 mV 3.1 mM Ca2+, obtained from a Woodhull type analysis). Currents were only stable in the absence of divalent cations and showed under these conditions a small time- and voltage-dependent component of activation. Single channel currents in cell-attached and inside-out patches had a conductance of 77.5 +/- 4.9 pS (n = 11) and reversed at +14.8 +/- 1. 6 11imV81i (n = 9) in the absence of divalent cations. The permeation sequence for monovalent cations through ECaC was Na+ > Li+ > K+ > Cs+ > NMDG+ which is identical to the Eisenmann sequence X for a strong field-strength binding site. It is concluded that the permeation profile of ECaC for monovalent cations suggests a strong field-strength binding site that may be involved in Ca2+ permeation and Mg2+ block.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms
  • Animals
  • Calcium Channels / metabolism*
  • Cations / metabolism*
  • Cell Line
  • Electrophysiology
  • Epithelium / metabolism
  • Extracellular Space / metabolism
  • Humans
  • Ion Channels / metabolism*
  • Kinetics
  • Magnesium / metabolism
  • Patch-Clamp Techniques
  • Rabbits
  • TRPV Cation Channels
  • Transfection

Substances

  • Calcium Channels
  • Cations
  • ECaC protein, Oryctolagus cuniculus
  • Ion Channels
  • TRPV Cation Channels
  • TRPV5 protein, human
  • Magnesium