Article: article d'un périodique ou d'un magazine.
Characterization of a whole-cell Ca2+-blockable monovalent cation current in isolated ectodermal cells of chick embryo.
Pflügers Archiv : European journal of Physiology
Date de publication
Publication types: Journal Article ; Research Support, Non-U.S. Gov't
The presence of a Ca2+-blockable monovalent cation current is demonstrated in isolated ectodermal cells of the chick embryo using the whole-cell patch-clamp method. In the absence of any stimulation, the whole-cell current is time independent and rectifies outwardly at membrane potentials higher than +40 mV. The outward current is neither carried by Cl- channels nor by K+ channels. Application of a Ca2+-free solution containing 1 mmol/l ethylenediaminetetraacetic acid (EDTA) elicits a large inward current and increases the outward current. The inward current can be carried by extracellular Li+, Na+, K+ and Cs+, but not N-methyl-D-glucamine. The Ca2+-blockable monovalent cation channel discriminates very poorly among these cations. The estimated number of channels per cell is around 2000. Extracellular protons block the inward Na+ current in the absence of extracellular Ca2+. The apparent negative logarithm of the dissociation constant for proton (pKH) at -100 mV is 5.8. Among 12 potential channel modulators, including verapamil and nifedipine, only quinine decreases the current. Quinine blocks this current with a dissociation constant, Kd, equal to 0.18 mmol/l, independent of the membrane potential. This study demonstrates the presence of a whole-cell Ca2+-blockable monovalent cation current in dissociated chick ectodermal cells with permeation properties similar to those observed at the single-channel level. Contrary to studies made of other tissues, we did not observe any blocking effect of verapamil and nifedipine on the Ca2+-blockable monovalent cation current.
Animals, Calcium/pharmacology, Calcium/physiology, Calcium Channel Blockers/pharmacology, Calcium Channels/drug effects, Calcium Channels/physiology, Cell Membrane Permeability/drug effects, Chick Embryo, Ectoderm/cytology, Glutamates/pharmacology, Hydroxides/pharmacology, Nifedipine/pharmacology, Protons, Quinine/pharmacology, Verapamil/pharmacology
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