N. Abi-gerges et al., Sequential changes in autonomic regulation of cardiac myocytes after in vivo endotoxin injection in rat, AM J R CRIT, 160(4), 1999, pp. 1196-1204
We report that in vivo injection of endotoxin (EDTX, 6 mg . kg(-1)) induces
cardiovascular alterations in rats that closely mimic the clinical situati
on, as assessed by in vivo hemodynamic measurements in anesthetized and con
scious, chronically instrumented animals. The patch-clamp technique was use
d to characterize the L-type calcium current (I-Ca) and its autonomic regul
ation in isolated cardiac myocytes. The density of I-Ca progressively decre
ased at 12 and 36 h after EDTX injection. However, the dihydropyridine (+/-
)Bay K 8644 (100 nM) enhanced I-Ca to levels similar to those in control an
d EDTX-treated myocytes. In addition, the net stimulatory effect of a beta-
adrenergic agonist (Isoproterenol) on I-Ca was increased 12 h after EDTX in
jection. This change in the beta-adrenergic effect declined 24 h later. The
potentiation in the beta-adrenergic stimulation of I-Ca was mimicked by L8
58051 (10 mu M), a direct activator of adenylyl cyclase, but not by IBMX (2
00 mu M), a phosphodiesterase inhibitor. Besides, the antiadrenergic effect
of acetylcholine on I-Ca was unchanged 12 h after EDTX injection, but Incr
eased 36 h after EDTX injection. These results support the hypothesis that
time-dependent changes in the adenylyl cyclase pathway in cardiac myocytes
may contribute, via the autonomic regulation of I-Ca, to the severity of my
ocardial dysfunction during sepsis.