Characterization of a whole-cell Ca2+-blockable monovalent cation current in isolated ectodermal cells of chick embryo.
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.
Sabovcik
R
R
Institut de Physiologie, Faculté de Médecine, Université de Lausanne, Switzerland.
Kucera
P
P
Prod'hom
B
B
D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002463:Cell Membrane Permeability / Q000187:drug effects; D002642:Chick Embryo; D004475:Ectoderm / Q000166:cytology; D005971:Glutamates / Q000494:pharmacology; D006878:Hydroxides / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D011522:Protons; D011803:Quinine / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D005971:Glutamates; D006878:Hydroxides; D011522:Protons; C014574:gamma-glutamylmethylamide; C031356:hydroxide ion; D011803:Quinine; D014700:Verapamil; D009543:Nifedipine; D002118:Calcium