Age-related changes in the transmembrane potential of isolated rabbit sino-atrial nodes and atria

Transmembrane potentials were recorded from single cells of the sino-atrial (S-A) node and right atrium isolated from rabbits of different ages (2 to 360 days old). In neonatal rabbit atria, the shape of pacemaker action potentials recorded from same S-A nodal cells were not regular, and action potentials showing a slow depolarisation during diastole were frequently recorded from the right atrium close to the crista terminalis. The atrial rate decreased, the maximal diastolic potential or resting potential and the size of the overshoot increased, and action potential durations were prolonged with age. Such alterations in the membrane potential related to age were not associated with changes in the atrial rate. The maximum rate of rise did not significantly differ in S-A nodes and right atria from rabbits of different ages. It may be concluded that the membrane permeability for K+ is increased and/or the permeability for Na+ is decreased during early postnatal period, resulting in alterations in the automaticity and parameters of the membrane potential. The relationship between maximum rate of rise and maximal diastolic potential or resting potential appears to be altered with age.