Comparison of the in vitro isolated strip methodology with the superfused strip technique

There are several methodologies available for determining the contractile effects of specific agents on isolated smooth muscle. The standard isolated bath technique utilizes strips mounted in a physiological buffer. The agent under study is added to the buffer and the response is recorded on a polygraph. The superfused strip technique utilizes strips in which buffer is pumped over the strip at relatively low flow rates. The agent under investigation is either infused into the stream of buffer bathing the tissue strip or administered directly onto the tissue. We have compared the response of these two methodologies using isolated strips of rabbit urinary bladder body. Isolated strips of rabbit urinary bladder were mounted in standard isolated baths containing 30 ml Tyrode's solution. The response of these strips to the autonomic agonists bethanechol, ATP, and isoproterenol were determined via cumulative addition at 5‐minute intervals. Similar strips were mounted as above, after equilibration, the Tyrode's was drained, and fresh oxygenated Tyrode's was pumped over the strip at a rate of 4 ml per minute. Flow was stopped and drugs were administered directly onto the tissue in 100‐μl aliquots. After either maximal response or 2 minutes, flow was resumed. Drugs were added at 10‐minute intervals. The results can be summarized as follows: 1) The superfused bladder strips responded to 100‐fold lower amounts of autonomic agonist than the strips in the isolated bath. 2) The maximum response to ATP (an agent that produces rapid desensitization) was threefold greater in the superfused model than in the bladder bath, and the rate of response of the tissues in the superfused system was significantly greater than in the isolated baths. In summary, the superfused isolated bladder preparation is an excellent methodology to use in specific investigations.