Action of potassium on neurochemical transmission at the cardiac adrenergic neuroeffector junction with aging.

The effect of age on potassium (K+)-induced norepinephrine release in the heart was studied in 6- and 24-month-old male Fischer-344 rats. Isolated hearts were perfused with Krebs-Ringer solution according to Langendorff method. K+ was employed as 2 ml bolus at the concentrations, of 70, 90, 100 and 120 microM. Norepinephrine content was measured by high pressure liquid-chromatography/electrochemical detection methodology. At each of the K- concentrations, the amount of norepinephrine released from preparations of 6-month-old animals was significantly greater than observed from preparations of 24-month-old animals. Since K(+)-induced release of norepinephrine is associated with calcium influx, the decrease in the capacity of K+ to cause norepinephrine release with age supports the hyothesis that diminution in transmitter release is due to altered calcium function.