Do differences develop in the electrogenesis of action potentials of the right and left ventricle of the guinea-pig heart during postnatal development.
Using the glass microelectrodes technique we measured the duration of action potentials (DAP) of the working myocardium of both ventricles in newborn and adult guinea-pigs in the steady state during stimulation with different frequencies and after a pause lasting 10--600 s. The resting membrane potential (RMP) value in the myocardium of newborn and adult animals was the same (85.3 mV and 86.3 mV respectively). The DAP of the right ventricular myocardium of newborn guinea-pigs was longer than in the left ventricle (p less than 0.02). Postnatally the action potentials (AP) of the left ventricular myocardium lengthened significantly, but the increase in the DAP of the right ventricular myocardium was very small, so that in adulthood the AP of the left ventricular myocardium were longer than those of the right ventricle (p less than 0.01). The frequency sensitivity of the guinea-pig myocardium was similar to the frequency sensitivity of the dog or cat myocardium; in both the neonatal and the adult myocardium it had the same character, but was quantitatively more pronounced in adult animals. An increase in the stimulation frequency from 0.5 Hz to 5 Hz slightly depressed the RMP. The first AP after the pause was longer and was proportional to the logarithm of the duration of the resting period. The effect of the pause was more noticeable in the myocardium of adult animals. Recovery of the AP from the effects of the pause was slow during stimulation with 1 Hz frequency and probably corresponded to recovery of intracellular calcium balance relationships. The results not only show dissimilarity of the neonatal and adult myocardium, but are also evidence of ontogenetically dependent differences in the character of electrogenesis in the left and right ventricular myocardium.
D000200:Action Potentials; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D004594:Electrophysiology; D006168:Guinea Pigs / Q000254:growth & development*; D006321:Heart / Q000254:growth & development* / Q000502:physiology; D006325:Heart Atria; D006352:Heart Ventricles; D006706:Homeostasis; D013997:Time Factors