Chloride movement across the wall of the rabbit submaxillary duct has been studied. It was shown that the chloride diffusion from blood to luminal side was determined primarily by the existing transmucosal potential difference. From the fact that the ouabain-poisoned duct showed symmetrical behavior with respect to the chloride diffusion potentials in both directions and the fact that the measured chloride flux behaved as predicted according to the Goldman equation, it was suggested that a single barrier, rather than a series membrane system, determined the chloride movement. The permeability coefficients for chloride, in the order of 5.5 x 10(-5) cm sce-1 are much larger than would be expected for cell membranes. These findings in combination with the observations that mannitol permeability is higher during chloride perfusion than during sulfate perfusion and the observed electron-microscopic changes favor the concept of the existence of an extracellular route in chloride diffusion. An equivalent electrical circuit is given in order to evaluate the contribution of the chloride shunt more quantitatively. Calculations showed that the ductal resistivity during sulfate perfusion has a value in the order of 434 omega cm2, while during chloride perfusion this value is lowered to 48 omega cm2, indicating that the ductal wall can change from a tight to a leaky epithelium. The implications of these findings are discussed.

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Unidirectional Na+ fluxes across ouabain-treated frog skins were measured at different applied voltages. The calculated influx/efflux ratios appear to deviate markedly from Ussing's flux-ratio equation. This means that interactions of Na+ ions with some component in the system occur. Possible mechanisms, responsible for this phenomenon, are indicated.