Effects of variations in extracellular pH on spontaneous contractile activity and response to nerve stimulation in smooth muscle from rat urinary bladder

The effects of variations in extracellular pH have been studied on rat detrusor muscle in vitro. At pH 7.4 a continuous low amplitude spontaneous contractile activity was found. At pH 6.75 the contractions became more regular with periods of relaxation between the contractions which had increased in amplitude. At pH 7.85 the reverse was found. The results are interpreted as a membrane effect of pH. No effect of pH on amplitudes of high-K(+)-induced contractures was found. Carbachol dose-response relations and maximal contraction amplitude to carbachol was similar at pH 7.4 and 6.75. A significant depression in response to nerve stimulation was, however, noted at pH 6.75. We suggest that, while the force output of the activated detrusor smooth muscle cell is unaffected by changes in extracellular pH, a prejunctional inhibition of nerve induced contraction might occur at low pH.