The effects of aging on responses to verapamil in isolated right atria

Potential senescence-related effects of verapamil were studied in spontaneously beating isometrically contracting right atria from 12 mature and 9 senescent male Fischer 344 rats. Verapamil 0-300 mcg/L prolonged spontaneous cycle length in all atria but produced significantly greater prolongation of spontaneous cycle length in the senescent vs mature right atria (p less than .03). In addition, cessation of spontaneous activity occurred more frequently and at lower concentrations in senescent vs mature atria. Recovery times from pacing at 3.5 pps and 5.0 pps also showed greater prolongation in response to verapamil in the senescent atria when compared to the mature right atria (p less than .004 and p less than .002). In contrast, the percent reduction of developed force produced by verapamil during pacing at 3.5 and 5.0 pps did not differ between senescent and mature atria.