Surface pH at the Basolateral Membrane of the Caecal Mucosa of Guinea Pig

Since the major mechanisms responsible for regulation of intracellular pH of enterocytes are located in the basolateral membrane, respective effects may be expected on pH in the compartment near the basolateral membrane. A method was established to estimate the pH at the basolateral membrane (pH b ) of isolated caecal epithelia of guinea pig using pH-sensitive fluorescein attached to lectin (lens culinaris). In the presence of bicarbonate and a perfusion solution-pH of 7.4, pH b was 7.70 ± 0.15. In the absence of bicarbonate or chloride as well as by inhibition of the basolateral Cl−-HCO− 3 exchange with H2-DIDS, pH b was reduced near to solution-pH. Inhibition of the basolateral Na+-H+ exchanger by adding a sodium- and bicarbonate-free, low-buffered solution increased pH b . Decrease of pH of serosal perfusion solution to 6.4 provoked a similar decrease of pH b to solution pH. Short-chain fatty acids (SCFA) added to the mucosal solution caused a slight decrease of pH b . SCFA added to the serosal side alkalized pH b . However, in the presence of bicarbonate pH b returned quickly to the initial pH b , and after removal of SCFA a transient acidification of pH b was seen. These responses could not be inhibited by MIA or H2-DIDS. We conclude that no constant pH-microclimate exists at the basolateral side. The regulation of the intracellular pH of enterocytes reflects pH b . The slightly alkaline pH b is due to the bicarbonate efflux. Data support the presence of an SCFA−-HCO− 3 exchange.