Effect of extracellular pH on contractile responses of the guinea-pig vas deferens

1. Effects of changing the pH of the bathing solution (7.0, 7.4 and 7.8) on the contractile response of the guinea-pig isolated vas deferens to ATP, noradrenaline (NA) and ATP in the presence of NA or electrical field stimulation (EFS) were investigated. 2. Low pH tended to augment the phasic contractile response to ATP (0.01-1 mmol/L), while high pH significantly reduced the contractile response to ATP. In contrast, low pH depressed the tonic contractile response to NA (0.1-10 mumol/L), while high pH augmented the response to NA. The contractile response to 1 mmol/L ATP was markedly potentiated in the presence of 0.1-10 mumol/L NA. The potentiated contractile response to ATP in the presence of NA was unaffected by changes in pH. 3. Electrical field stimulation produced a biphasic contractile response. Low pH enhanced the initial rapid phasic contractile response to EFS, while high pH depressed the response. In contrast, the second slow tonic contractile response to EFS was unaffected by changes in pH. 4. These findings may indicate that the phasic contractile response to EFS is mainly caused by ATP while the tonic contractile response is a synergistic response to ATP and NA concomitantly released from sympathetic nerve terminals.