Af. James et al., DISTRIBUTION OF CAMP-ACTIVATED CHLORIDE CURRENT AND CFTR MESSENGER-RNA IN THE GUINEA-PIG HEART, Circulation research, 79(2), 1996, pp. 201-207
Guinea pig ventricular myocytes exhibit a Cl--selective current regula
ted by the cAMP-dependent pathway. We have investigated the distributi
on of cAMP-activated Cl- channel current density and cystic fibrosis t
ransmembrane-conductance regulator (CFTR) mRNA in three regions of the
guinea pig heart: the atrium, and the epicardium and endocardium of t
he 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 mu mol/L) ac
tivated Cl--selective currents in all ventricular myocytes and 21% of
atrial myocytes examined. The conductance density, estimated as the ou
tward chord conductance normalized to cell capacitance, was greatest i
n epicardial myocytes (79.8 +/- 8.3 pS/pF, n = 21) and significantly l
ower 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 expr
ession levels were investigated by competitive reverse-transcribed pol
ymerase chain reaction. The regional distribution of the mRNA levels w
as similar to that of the Cl- conductance density, ie, highest in the
epicardium (23 230 +/- 1840 molecules/mu gl total RNA, n = 3), signifi
cantly lower in endocardium (10 610 +/- 780 molecules/mu g total RNA,
n = 3), and lowest in atrium (1450 +/- 290 molecules/mu g total RNA, n
= 3). The data indicate that regional differences in CFTR mRNA expres
sion in the guinea pig heart are responsible, at least in part, for th
e regional differences in cAMP-activated Cl- current density.