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Characterization of voltage‐dependent calcium channels expressed in Xenopus oocytes injected with mRNA from rat heart.
Author(s) -
Lory P,
Rassendren F A,
Richard S,
Tiaho F,
Nargeot J
Publication year - 1990
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 - 10.1113/jphysiol.1990.sp018246
Subject(s) - xenopus , dihydropyridine , agonist , bay k8644 , chemistry , voltage clamp , biophysics , barium , endocrinology , voltage dependent calcium channel , medicine , calcium , receptor , membrane potential , biology , biochemistry , inorganic chemistry , organic chemistry , gene
1. The properties of voltage dependent cardiac Ca channels expressed in Xenopus laevis oocytes after injection of mRNA from rat heart were investigated using the double‐microelectrode voltage‐clamp technique. 2. Endogenous Ba current (IBa,E) and expressed cardiac Ba current (IBa,C) were studied at various external concentrations of barium (Ba2+). These two entities could be distinguished by their amplitude and their pharmacology. IBa,C was more sensitive to the inorganic Ca channel blocker manganese (Mn2+). The contaminant IBa,E presented properties of voltage dependence identical to IBa,C, but was negligible in the presence of a low external Ba2+ concentration (2 mM). 3. In 2 mM‐Ba2+, IBa,C activated at ‐35 mV, peaked at ‐14 mV, and reversed at +26 mV. Steady‐state inactivation properties, in consideration of the half‐inactivation potential of ‐35 mV, were also typical of L‐type Ba currents. However, the decay of IBa,C was very slow (time constant of inactivation near 600 ms). No evidence for the expression of cardiac transient Ca channels (T‐type) was found. 4. IBa,C was enhanced after exposure to the 1,4‐dihydropyridine (DHP) agonist Bay K 8644. The enhancement of IBa,C was voltage dependent (maximum at ‐30 +/‐ 5 mV) and associated with a slowing in current decay. Current‐voltage and concentration‐response curves obtained for various Ba2+ concentrations revealed an antagonism between external Ba2+ and the 1,4‐DHP agonist Bay K 8644. Similar results were found using the (‐)Bay K 8644 pure agonist isomer. 5. We conclude that oocytes injected with mRNA from rat heart expressed only the high threshold, long‐lasting or L‐type Ca channels. The availability of expressed L‐type Ca channels for quantitative pharmacological studies using low Ba2+ concentration has been demonstrated.