The role of the lateral intercellular spaces in the control of ion permeation across the rabbit gall bladder.

Diffusion potentials and conducatance measurements were used to evaluate the changes in permeability of the rabbit gall bladder when the lateral spaces were 1) closed by the addition of sucrose to the mucosal fluid, and 2) dilated by the addition of sucrose to the serosal fluid. The results showed that when the lateral spaces were closed (less than 10 nm/ 1) there was a significant decrease in the conductance of the epithelium, and 2) the ion selectivity of the epithelium moved towards the free solution sequence. The conductance decreased from 31 to 13 mmhos/cm2, and the selectivety changed from Na(1) greater than Li(0.92) greater than Cs(0.85) to Cs(1.27) greater than Na(1) greater than Li(0.84). Neither dilation of the spaces to greater than 1.5 mum nor addition of sucrose to both sides of the gall bladder changed the conductance or the ion selectivity. These results are consistant with the hypothesis that in the gall bladder the major barrier to ion permeation across the epithelium lies in 1) the tight junctions, when the lateral spaces are dilated, 2) the lateral spaces when the spaces are collapsed, and 3) a combination of both the spaces and the junctions when the spaces are reduced much below 0.5 mum. Consequently the status of the lateral intercellular spaces has to be taken into account when assessing the mechanisms of ion permeation across low resistance epithelia.