Interrelationship between sugar-evoked increases in transmural potential difference and sugar influxes across the...

The relationship between changes in the transmural potential induced by actively transported sugars(deltaPDs) and influxes of the sugars(Js's) was investigated in the isolated guinea pig small intestine. Under the condition that medium electrical conductivity. remains unchanged, deltaPD and Js were closely correlated, e.g., both showed very similar patterns of regional difference along the intestine, and the values of the half saturation concentration (Km) for a sugar estimated from electrical and flux measurements were nearly identical. No such correlation was observed when medium conductivity varied. However, a simple correction of the sizes of deltaPDs for medium conductivity restored a close parallelism between deltaPDs and Js's. The sugar-induced increase in Na+ flux estimated from the increase in short-circuit current varied in parallel with Js regardless of the medium conductivity, and a fixed stoichiometrical relationship (approximately one-to-one coupling) was seen between Na+ and sugar fluxes. It is concluded that the dominant factor affecting the interrelation between deltaPD and Js is the resistance of the paracellular shunt which is directly proportional to medium electrical conductivity