A hyperpolarization activated inward current (If) is present in infant ventricular myocytes
2003
If was shown to be present in adult
human atrial and ventricular myocytes but data obtained from
infant myocytes are lacking. We have studied
If in isolated ventricular myocytes from
children undergoing surgical correction of tetralogy of Fallot
(TOF; n = 5; mean age: 15.3 months). All recordings were made
with the patch clamp technique in the whole cell mode at a
temperature of 36–37 °C. A modified Tyrode solution containing 25
mM KCl was used to amplify If.
Considering If to be present when its
current density at –120 mV was greater than 0.5 pA/pF,
If could be found in 28 out of 32
myocytes (88%). The mean current density was –2.01 ± 0.3 pA/pF
(mean ± S.E.M.). First current activation occurred at –70 mV and
If could be reversibly inhibited by
superfusing the myocytes with CsCl (2 mM). Half maximal
activation (V1/2) of
If was at –80.3 ± 1.0 mV (n = 28).
Beta-adrenergic receptor stimulation with isoproterenol (1 µM)
caused an acceleration of current activation and a shift of
V1/2 by 7.88 ± 1.8 mV (n = 10) to less
negative potentials. This study provides first evidence that the
hyperpolarization-activated pacemaker current
If is present in infant human ventricular
myocytes. Our results suggest that If in
ventricle of infants suffering from TOF has similar properties
as If in adult ventricle.
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