AGE-RELATED-CHANGES IN CARDIAC NOREPINEPHRINE RELEASE - ROLE OF CALCIUM MOVEMENT

The purpose of this study was to determine if the age-related decrease in norepinephrine (NE) release from cardiac adrenergic nerve terminal s is due to a defect in Ca2+ movement into the nerve terminal or to an alteration in Ca2+ activation of intracellular events leading to NE r elease. NE release was assessed in cardiac synaptosomes prepared from 6- and 24-month-old male F344 rats. K+-induced NE release was signific antly greater in young vs old rats. Raising extracellular [Ca2+] incre ased NE release, but NE release always remained higher in the younger animals. lonomycin, a Ca2+ ionophore, induced NE release from cardiac synaptosomes, and there was no age difference in the response. The age -related reduction in NE release induced by K+ and the capacity of ion omycin to induce similar NE release in young and old cardiac synaptoso mes points to a reduction in Ca2+ movement during depolarization.