The contribution of a chloride shunt to the transmucosal potential of the rabbit submaxillary duct

Summary

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 ouabainpoisoned 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 5.5×10⁻⁵ cm sec⁻¹ are much larger than would be expected for cell membranes. These findings in combination with the observation 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 Ω cm², while during chloride perfusion this value is lowered to 48 Ω cm², indicating that the ductal wall can change from a tight to a leaky epithelium. The implications of these findings are discussed.