Age-related changes in the rat detrusor muscle: the contractile response to inorganic ions

The effect of age on in vitro rat bladder responsiveness function in inorganic ions, CaCl2, KCl, BaCl2 and MgCl2, was investigated, and the results were compared between young (six months old) and aged (16 and 24 months old) rats. In the aged bladders the contractile strength and contractile speed responding to CaCl2 were significantly less compared to the young. On the other hand, the muscle contraction of the three groups following depolarization of the cell membrane by adding KCl and BaCl2 did not differ significantly. The change in muscle relaxation responding to MgCl2 was also insignificant. These results suggest that although contractile and relaxation mechanisms of the detrusor muscle per se are not affected by an aging process, the contractile ability which is related to calcium ion is impaired in the aged rats. It is likely that decreased membrane permeability to calcium ions and/or the change in the intracellular contractile mechanisms related to calcium ions may account for the decreased muscle contractility in the aged rats.