EFFECTS OF BICARBONATE REMOVAL ON THE SPONTANEOUS MECHANICAL ACTIVITY OF THE GUINEA PIG UTERUS

Abstract

1. Effects of bicarbonate removal and of decreasing external pH on the mechanical and electrical activities in isolated strips of the guinea pig uterus were investigated.2. When bicarbonate was reduced at 37°C, a high degree of contractile activity was observed, which was associated with high frequency spike activity. However, when the same experiment was repeated at 21°C, the activity was suppressed. These sustained contractions were produced whether the HCO-3-free solution was acid (pH: about 6) in the presence of 3% CO2, or the solution was alkaline (pH: about 8) in the absence of CO2.3. When the pH of the solution was decreased to 6 by 5mM tris malate buffer, the mechanical activity was also increased in the presence of 15.5mM HCO-3.4. In low Cl- (7 mm) Krebs solution the mechanical activity depended on the substitute for Cl-: substitution with isethionate reduced or stopped the activity, while substitution with NO-3 increased the activity. The increase in activity on HCO-3 removal was less in isethionate solution and much larger in NO-3 solution.5. At a lower temperature (21°C), HCO-3 removal suppressed the activity when O2 containing 3% CO2 was bubbled through the solution.6. It is suggested that HCO-3 removal and acidification increase Cl-permeability of the membrane and that this leads to high spontaneous activity. It is also possible that modification of the external buffer system may affect the internal pH and metabolism, which in turn modifies spontaneous activity.