Age-related changes in rat atrial sensitivity to lidocaine

The effects of increasing age were studied on rat atrial sensitivity to lidocaine by means of intracellular microelectrode recording of transmembrane electrical activity. Under control conditions, atrial resting potential and the maximum rate of rise of phase 0 (Vmax) were not influenced by increasing age (1 month to 24 months). However, the amplitude of the action potential and of the overshoot, and the duration of the action potential and the plateau phase decreased as a function of age. Lidocaine hydrochloride, 5 mg/L, did not alter resting potential, but decreased the amplitude of the action potential and of the overshoot, decreased the frequency of occurrence of an overshoot, decreased Vmax, and increased action potential duration and plateau duration. The effects of lidocaine to abolish the overshoot and prolong the duration of the action potential and the plateau phase increased with increasing age. Thus, it has been demonstrated that electrophysiological properties of rat atrial muscle undergo alterations in relation to increasing age. These alterations may be responsible for the observed age-related changes in atrial sensitivity to lidocaine.