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Pore properties and ionic block of the rabbit epithelial calcium channel expressed in HEK 293 cells
Author(s) -
Vennekens Rudi,
Prenen Jean,
Hoenderop Joost G. J.,
Bindels René J. M.,
Droogmans Guy,
Nilius Bernd
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.0183l.x
Subject(s) - divalent , chemistry , permeation , biophysics , extracellular , bapta , patch clamp , ion transporter , membrane potential , reversal potential , calcium , lanthanum , analytical chemistry (journal) , inorganic chemistry , biochemistry , chromatography , membrane , receptor , organic chemistry , biology
1 We have used the whole‐cell patch‐clamp technique to analyse the permeation properties and ionic block of the epithelial Ca 2+ channel ECaC heterologously expressed in human embryonic kidney (HEK) 293 cells. 2 Cells dialysed with 10 mM BAPTA and exposed to Ca 2+ ‐containing, monovalent cation‐free solutions displayed large inwardly rectifying currents. Their reversal potential depended on the extracellular Ca 2+ concentration, [Ca 2+ ] o . The slope of the relationship between reversal potential and [Ca 2+ ] o on a logarithmic scale was 21 ± 4 mV, compared with 29 mV as predicted by the Nernst equation ( n = 3‐5 cells). 3 Currents in mixtures of Ca 2+ and Na + or Ca 2+ and Ba 2+ showed anomalous mole fraction behaviour. We have described the current‐concentration plot for Ca 2+ and Na + by a kinetic permeation model, i.e. the ‘step’ model. 4 Extracellular Mg 2+ blocked both divalent and monovalent currents with an IC 50 of 62 ± 9 μM ( n = 4 ) in Ca 2+ ‐free conditions and 328 ± 50 μM ( n = 4‐9 ) in 100 μM Ca 2+ solutions. 5 Mono‐ and divalent currents through ECaCs were blocked by gadolinium, lanthanum and cadmium, with a blocking order of Cd 2+ >> Gd 3 + > La 3 + . 6 We conclude that the permeation of monovalent and divalent cations through ECaCs shows similarities with L‐type voltage‐gated Ca 2+ channels, the main differences being a higher Ca 2+ affinity and a significantly higher current density in micromolar Ca 2+ concentrations in the case of ECaCs.