Distribution of cAMP-activated chloride current and CFTR mRNA in the guinea pig heart.
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 mumol/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 (23230 +/- 1840 molecules/microgram total RNA, n = 3), significantly lower in endocardium (10610 +/- 780 molecules/microgram total RNA, n = 3), and lowest in atrium (1450 +/- 290 molecules/microgram 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.
James
A F
AF
Department of Cellular and Molecular Physiology, National Institute for Physiological Sciences, Japan.
Tominaga
T
T
Okada
Y
Y
Tominaga
M
M
D000818:Animals; D001483:Base Sequence; D018118:Chloride Channels / Q000502:physiology*; D000242:Cyclic AMP / Q000502:physiology*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics*; D004553:Electric Conductivity; D006168:Guinea Pigs; D015335:Molecular Probes / Q000235:genetics; D008969:Molecular Sequence Data; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism*; D014018:Tissue Distribution; D014158:Transcription, Genetic
D018118:Chloride Channels; D015335:Molecular Probes; D012333:RNA, Messenger; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000242:Cyclic AMP