Article

Differences in outward currents between neonatal and adult rabbit ventricular cells.

Centro de Investigaciones Biomédicas, Universidad de Colima, Mexico.
The American journal of physiology 04/1994; 266(3 Pt 2):H1184-94. pp.H1184-94
Source: PubMed

ABSTRACT In adult rabbit ventricular preparations, action potential duration is significantly increased when stimulation frequency is increased from 0.1 to 1.0 Hz. In neonatal preparations, a similar change in stimulation frequency produced no significant increase in action potential duration. To identify the ionic basis for this difference, we studied different outward currents in single myocytes from papillary muscle and from epicardial tissue of adult and neonatal rabbits. The densities of the outward currents in neonatal cells were about one-half of the current density in adult cells. The density of the voltage-activated transient outward current (I(to1)) was smaller in cells from papillary muscle than in cells from epicardium in adult and newborn rabbits. We found major differences in the kinetic behavior of I(to1) between adult and neonatal cells: 1) the rate of apparent inactivation was faster in neonatal cells, and 2) the recovery from inactivation was significantly faster in neonatal cells, with a time constant of 113 vs. 1,356 ms. We propose that this marked difference in the recovery from inactivation of I(to1) is the basis for the difference in frequency dependence of action potential duration.

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Keywords

action potential duration
 
adult cells
 
adult rabbit ventricular preparations
 
apparent inactivation
 
different outward currents
 
epicardial tissue
 
Hz
 
inactivation
 
ionic basis
 
kinetic behavior
 
neonatal cells
 
neonatal preparations
 
neonatal rabbits
 
newborn rabbits
 
outward currents
 
papillary muscle
 
similar change
 
single myocytes
 
stimulation frequency
 
voltage-activated transient outward current