Peptidergic Control of Transport in the Teleost Gill

Abstract

The teleost gill has a key position in the history of the study of epithelial ion transport — the first unequivocal demonstration of ion transport in vitro was the experiments on chloride excretion by the marine teleost gill performed by Ancel Keys more than 50 years ago (Keys 1931a,b; Bateman and Keys 1932). However, as a tissue to study the mechanisms of transport, it is far from “ideal”. For example, both its structural complexity and physiological characteristics create problems for the investigator, not least in the measurement of the active component of the overall transport of ions across the epithelium. Essentially, in the determination of active ion transport in the marine teleost gill, the use of isotopes is inappropriate, and the measurement of short-circuit current, impossible. Measurements of branchial isotopic fluxes of either sodium or chloride show very large bidirectional exchanges (Motais et al. 1966). These fluxes of sodium and chloride in both directions across the epithelium are clearly of no significance for the fish under normal (i.e. steady state) circumstances, but they are usually so large that they obscure the physiologically relevant active fluxes which may make up only 5%–10% of the total unidirectional fluxes. The difficulties of identifying usually small changes in this 5%–10% of the total measured flux are obvious and strongly mitigate against this method as a “technique of choice” for the marine teleost gill, despite the widespread use of such an approach in transport studies generally.