Chapter 16 The Effects of Voltage Clamping on Ion Transport Pathways in Tight Epithelia

Abstract

This chapter describes and presents evidence that the resistance of the shunt pathway in toad urinary bladder and skin changes during the passage of current and that this change is voltage and time dependent. The studies in toad urinary bladder reported in this chapter, however, indicate that there is no change in the resistance of the cellular pathway. These studies make it clear that in both toad skin and toad urinary bladder the decrease in resistance during passage of a transepithelial pulse is accompanied by an increase in the transepithelial flux through the extracellular pathway. The increase in transepithelial serosa-to-mucosa sodium flux induced by voltage or current clamping indicates an increase only in the conductance of the paracellular pathway. Because the conductance of the paracellular pathway is a function, at least in part, of the transport properties of the tissue, one way to reconcile the changes described in the chapter might be to assume that the inhibition of transport brought about by voltage clamping directly affects the shunt pathway. However, it is not yet clear that the change in conductance represents a universal phenomenon in other tight epithelia despite the fact that toad skin seems to share the same characteristics as the urinary bladder.