Age related differences in the response to acidosis, hypoxia, and hyperkalaemia in canine cardiac Purkinje fibers.
OBJECTIVE
In the clinical setting, the response of adult and neonatal cardiac rhythms to hypoxia and to acidosis differs, the former leading to tachyarrhythmias and the latter to bradyarrhythmias. In this study, the aim was to determine whether a cellular electrophysiological substrate could be identified to explain the clinical observation.


METHODS
Conventional microelectrode techniques were used to study the electrophysiological responses of automatic Purkinje fibres to acidosis, hypoxia, and hyperkalaemia individually.


RESULTS
Adult Purkinje fibres showed decreases in maximum diastolic potential, activation voltage, and automaticity as pH was decreased from 7.3 to 6.1. Triggered activity due to early afterdepolarisations developed in 70% of adult Purkinje fibres at pH 6.1. Neonatal Purkinje fibres showed decreased automaticity as pH decreased and, in contrast to adults, quiescence occurred at pH 6.1 At PO2 < 2.9 kPa automaticity decreased significantly in adult Purkinje fibres, whereas neonatal fibres were unaffected. The effect of raising [K+]o was comparable at both ages.


CONCLUSIONS
The response to acidosis and to hypoxia differs significantly between neonatal and adult Purkinje fibres and may explain some developmental differences in the expression of cardiac arrhythmias.
Geller
J C
JC
Department of Pharmacology, Columbia University, New York, NY 10032.
Rosen
M R
MR
D000138:Acidosis / Q000503:physiopathology*; D000375:Aging / Q000502:physiology*; D000818:Animals; D004285:Dogs; D004594:Electrophysiology; D005260:Female; D006947:Hyperkalemia / Q000503:physiopathology*; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D011690:Purkinje Fibers / Q000503:physiopathology*