[Pharmacological experiments in the aged rat urinary bladder. Responses to inorganic ions (Ca2+, K+, Ba2+, Mg2+)]

We studied in vitro the change in muscle contractility and ion permeability of cell membrane of aged rat urinary bladder (16 and 24 months old) and compared with young rat bladder (6 months old). The results are summarized as follows: 1. In aged rat bladder the contractile response to Ca2+ was significantly decreased comparing to young rat bladder. The speed of muscle contractility was also significantly slower in aged rat bladder. 2. There was no significant change in muscle contractility in response to K+ and Ba2+ among the 3 age groups, which indicated that contractile force of aged rat bladder per se was not impaired. 3. Mg2+ relaxed the detrusor muscle in a dose-dependent manner. The magnitude of the response was not different between aged and young rat bladders. It is concluded that the response of aged rat urinary bladder to Ca2+ was decreased in contraction strength and contraction speed. This finding seems to suggest that membrane permeability of Ca2+ has been compromised, which may account for the impaired detrusor contractility frequently observed in elderly persons.