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Effects of dopamine on L‐type Ca 2+ current in single atrial and ventricular myocytes of the rat
Author(s) -
Zhao H,
Matsuoka S,
Fujioka Y,
Noma A
Publication year - 1997
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0701250
Subject(s) - medicine , phentolamine , endocrinology , isoprenaline , dopamine , chemistry , propranolol , contraction (grammar) , stimulation , dopamine receptor , biology
The effects of dopamine on the L‐type Ca 2+ current ( I Ca,L ) of both atrial and ventricular single myocytes and on the force of contraction of atrial trabeculae in rat heart were investigated. Dopamine increased atrial I Ca,L at concentrations higher than 1 μ M , but had little or no effect on I Ca,L at lower concentrations. The increase in I Ca,L at high concentrations was reversed by propranolol and acetylcholine, but not by phentolamine. Activation and inactivation kinetics of I Ca,L were not altered by dopamine. In rat ventricular myocytes in which the D 4 receptor mRNA does not express, dopamine (20–100 μ M ) also increased the I Ca,L amplitude and propranolol reversed this effect. Clozapine, a potent D 4 receptor antagonist, blocked the augmenting effect of dopamine on I Ca,L . However, this effect could be explained by β‐antagonism, since clozapine also inhibited the isoprenaline effect. In the atrial trabeculae, the increase in contraction by dopamine (1 to 30 μ M ) was reversed by 1 μ M propranolol, but not by 2 μ M phentolamine. Low doses of dopamine (0.01 to 0.3 μ M ) did not affect the contraction in the controls or during a modest stimulation of the β‐adrenoceptor with 0.01 μ M isoprenaline. These results indicate that the positive inotropic action of dopamine is mediated through direct stimulation of the β‐adrenoceptor in both atrial and ventricular myocytes. Involvement of D 4 receptor appears unlikely in the regulation of the atrial contraction.