© 1996 American Heart Association, Inc.
Articles |
Distribution of cAMP-Activated Chloride Current and CFTR mRNA in the Guinea Pig Heart
the Department of Cellular and Molecular Physiology, National Institute for Physiological Sciences, Japan.
Correspondence to Dr M. Tominaga, Department of Cellular and Molecular Physiology, National Institute for Physiological Sciences, Myodaiji-cho, Okazaki 444, Japan.
Guinea pig ventricular myocytes exhibit a Cl--selective current regulated by the cAMP-dependent pathway. We have investigated the distribution of cAMP-activated Cl- channel current density and cystic fibrosis transmembrane-conductance regulator (CFTR) mRNA in three regions of the guinea pig heart: the atrium, and the epicardium and endocardium of the free wall of the left ventricle. The regional differences in the Cl- current density were investigated in enzymatically isolated myocytes using the whole-cell patch-clamp technique. Forskolin (1 µmol/L) activated Cl--selective currents in all ventricular myocytes and 21% of atrial myocytes examined. The conductance density, estimated as the outward chord conductance normalized to cell capacitance, was greatest in epicardial myocytes (79.8±8.4 pS/pF, n=21) and significantly lower in endocardial (59.8±9.5 pS/pF, n=22) and atrial (10.9±5.0 pS/pF, n=38) myocytes. The regional differences in CFTR mRNA expression levels were investigated by competitive reverse-transcribed polymerase chain reaction. The regional distribution of the mRNA levels was similar to that of the Cl- conductance density, ie, highest in the epicardium (23 230±1840 molecules/µg total RNA, n=3), significantly lower in endocardium (10 610±780 molecules/µg total RNA, n=3), and lowest in atrium (1450±290 molecules/µg total RNA, n=3). The data indicate that regional differences in CFTR mRNA expression in the guinea pig heart are responsible, at least in part, for the regional differences in cAMP-activated Cl- current density.
Key Words: Cl- channel • CFTR • cardiac myocyte • guinea pig • competitive RT-PCR
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