Agonist-induced Ca 2+ mobilization in the rat submandibular gland during aging and subsequent to chronic propranolol treatment

Abstract

The effects of age and chronic propranolol treatment on the agonist-induced rise in intracellular free Ca 2+ ([Ca 2+] i), an index for the coupling of receptor-second messenger generation, was studied using a dispersed rat submandibular gland preparation. Muscarinic stimulation (10 μm carbachol) caused a rapid ( T 1 2 < 2 s ) and dramatic (∼ 4.5-fold) rise in [Ca 2+] i followed by a lower sustained increase (∼ 3-fold) in [Ca 2+] i as measured directly with the Ca 2+-sensitivie fluorescent probe, fura-2. The magnitude and the rate of increase of the initial rise in [Ca 2+ i and the level of the sustained increase in [Ca 2+] i were not different between 2- and 21-month-old rats. Stimulation in a Ca 2+-free medium reduced the initial agonist-induced increase in [Ca 2+] i by ∼ 35–40%, while the sustained increase was abolished by the removal of extracellular Ca 2+ from cells in both young and old rats. Chronic treatment for 30 days with 20 mg/kg propranolol, a β-adrenergic antagonist, did not significantly alter the ability of dispersed submandibular cells in old rats to mobilize Ca 2+ during agonist stimulation or influence the in vivo stimulated gland output. These results suggest that the agonist-induced rise in [Ca 2+] i is not altered by aging or by chronic treatment of aged rats with propranolol and, therefore, receptor-second messenger coupling remains intact.