Whole-cell and single channel monovalent cation currents through the novel rabbit epithelial Ca2+ channel ECaC.
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.
Nilius
B
B
Department of Physiology, Campus Gasthuisberg, Katholieke Universiteit, Leuven, Leuven, Belgium. bernd.nilius@med.kuleuven.ac.be
Vennekens
R
R
Prenen
J
J
Hoenderop
J G
JG
Bindels
R J
RJ
Droogmans
G
G
D000465:Algorithms; D000818:Animals; D015220:Calcium Channels / Q000378:metabolism*; D002412:Cations / Q000378:metabolism*; D002460:Cell Line; D004594:Electrophysiology; D004848:Epithelium / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D007473:Ion Channels / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011817:Rabbits; D050916:TRPV Cation Channels; D014162:Transfection
D015220:Calcium Channels; D002412:Cations; C118497:ECaC protein, Oryctolagus cuniculus; D007473:Ion Channels; D050916:TRPV Cation Channels; C492239:TRPV5 protein, human; D008274:Magnesium