CHARACTERIZATION OF CONDUCTIVE PATHWAYS IN GUINEA-PIG DISTAL COLON INVITRO

Isolated mucosal sheets of guinea pig distal colon were studied in vitro in Ussing-type chambers, using a computer-controlled voltage clamp. A conductance of 8-12 mS[millisiemens]/cm2 and spontaneous variations of the potential difference (Vt, -4 to +6 mV) and the short-circuit current (Isc, -1.6 to +1.5 .mu.eq .cntdot. cm-2 .cntdot. h-1) were observed. With use of a green feed diet these variations could be entirely attributed to the rate of Na transport. Unidirectional Na and Cl fluxes were measured, and for Na, K and Cl transport the individual conductances and directions were estimated from the changes in Vt and Isc, using the appropriate blockers amiloride, barium and piretanide. The sum of the electrogenic Na, K and Cl transport determined the spontaneous electrical behavior of this epithelium. Na transport was further characterized with transepithelial and transapical current-voltage relations. Apical Na entry occurred by diffusion, intracellular Na activity was 12 mM, and apical Na permeability was calculated as 0.02 cm/h. This study apparently represents the 1st in vitro investigation of electrogenic transport in this epithelium and shows that it closely resembles transport mechanisms found in rabbit colon.