Human intestinal potential difference: recording method and biophysical implications.

1. The transmural electrical potential difference (PD) of the intact human small intestine was recorded with close attention to electrical symmetry, shielding from electro-magnetic waves and correction for junction potentials. 2. The PD is -12 mV (mucosa-negative) in the fasting jejunum and ileum and does not change during perfusion with isotonic NaCl. 3. Absorption of Na and Cl appears to be non-electrogenic and the 'resting' PD is probably generated by active anion secretion of fasting intestinal contents. 4. Diffusion potentials during isotonic D-mannitol perfusion indicated higher cation selectivity in the ileum than in the jejunum. 5. The calculated contribution of a free-solution path to total paracellular permeability is 55% in the jejunum but only 15% in the ileum. 6. No 'streaming' potential was detected during osmotic water flow, suggesting that the cation-selectivity of the channels is temporarily inactivated during dilatation of the lateral intercellular space.