Effects of aging on ionic movements of atrial muscle.

The effect of age on ion concentrations and fluxes in cardiac muscle was examined. Left atria from rats of 1, 3, 6, 12, 24, and 28 months of age were analyzed for content of total water, sodium and potassium, for 14C-inulin space and for 22Na and 42K influx and efflux rates. Animals of 3 and 24 months of age showed a small but significantly greater water content than those of the other age groups. The inulin space, after a small nonsignificant fall between 1 and 3 mo, increased significantly at 6 mo, then leveled off through 28 mo. Intracellular sodium (Na)1, and potassium (K)1 concentrations were calculated. (Na)1 showed a significant increase from 1 to 3 mo, decreased significantly at 6 mo, and then leveled off. (K)1 exhibited an initial significant decrease from 1 to 3 mo followed at 6 mo by a significant increase which remained unchanged through 28 mo. Trend analyses of the Na influx rates showed that a significant increase with age occurred, except for a decrease at 24 mo. Potassium influx rates remained relatively constant at all ages. Sodium efflux appeared to be multiexponential, with at least two distinct rate constants (k1 and k2). Potassium efflux steadily decreased as a function of age. The results are discussed with reference to possible consequences of aging on cardiac physiology and reactivity to pharmacological agents.