E. Cerbai et al., Influence of postnatal-development on I-f occurrence and properties in neonatal rat ventricular myocytes, CARDIO RES, 42(2), 1999, pp. 416-423
Citations number
31
Categorie Soggetti
Cardiovascular & Respiratory Systems","Cardiovascular & Hematology Research
Objective: I-f is a hyperpolarization-activated current, which plays a key
role in determining the spontaneous rate of cardiac pacemaker cells. We hav
e previously shown that I-f is also expressed in left ventricular myocytes
isolated from spontaneously hypertensive rats; in these cells, its occurren
ce and density is linearly related with the severity of myocardial hypertro
phy. Since hypertrophy induces a re-expression of genes encoding fetal prot
eins, we investigated changes in I-f properties during post-natal developme
nt. Methods: Fresh ventricular myocytes were enzymatically isolated from th
e heart of 1-2- to 28-day-old Wister mts. The whole-cell configuration of t
he patch-clamp technique was employed to record the action potential and I-
f. Results: Membrane capacitance, an index of cell size, progressively incr
eased from 13+/-1 pF at 1-2 days to 66+/-4 pF at 28 days of age (p<0.01). A
t 1-2 days, a cesium-sensitive hyperpolarization-activated inward current (
I-f) was recorded in the majority of tested cells (n=51). The midpoint of t
he activation curve (V-1/2) was -78+/-2 mV (n=32), and specific current con
ductance of fully activated I-f (g(f,max)) was 60+/-11 pS/pF. Reversal pote
ntial (V-rev) measured by tail-current analysis was -24+/-3 mV(n=8). Reduct
ion of extracellular Na+ from 140 to 35 mM or extracellular K+ from 25 to 5
.4 mM caused a shift of -12+/-1 mV(n=3) or -11+/-2, mV(n=5) of V-rev, respe
ctively. Occurrence of I-f decreased with aging, being present in 64%, 48%
and 32% of cells at 10, 15 and 28 days, respectively. When present, I-f den
sity was significantly smaller than at 1-2 days (p<0.05), reaching a value
of 8+/-2 pS/pF at 28 days. However, V-1/2 did not change in the older rats,
being -80+/-2, -83+/-4 and -85+/-3 mV at 10, 15 and 28 days, respectively.
V-rev at 10 and 15 days was -27 and -28 mV,respectively, thus suggesting t
hat channel selectivity did not change. Conclusions: The pacemaker current,
I-f, is expressed in ventricular myocytes from neonatal rats and progressi
vely disappears; when present, it shows electrophysiological properties sim
ilar to I-f re-expressed in hypertrophied adult rat ventricular myocytes. T
hus, it is likely that the occurrence of I-f in ventricular myocytes of hyp
ertrophied and failing hearts is due to the re-expression of a fetal gene.
(C) 1999 Elsevier Science B.V. All rights reserved.