Introduction: trends in epithelial transport and control.

Abstract

ABSTRACT Osmotic and ionic regulation ultimately depend on epithelial transport mechanisms and their control in most metazoans, although intracellular osmotic adjustments are probably more important in marine osmoconformers. There are a great variety of osmoregulatory organs throughout the animal kingdom and physiological information about many of these is still so incomplete that it seemed inappropriate to attempt a comprehensive review or synthesis of osmoregulation in a small discussion meeting of this type. However, given the general conservative nature of many cellular processes during the course of animal evolution, we might anticipate common protein carrier mechanisms which are organized and controlled in a limited number of ways within most epithelia. A number of such general concepts and models of epithelial transport have developed over the last ten years and these should prove useful in the future when less well studied osmoregulatory organs are investigated. With this in mind, we have included in this volume reports on some of the most intensively studied epithelia having a range of different regulatory functions. These papers will indicate (1) the types of primary and secondary transport mechanisms which are now well established and partially characterized, (2) their typical asymmetrical distribution in epithelia, and (3) cellular processes associated with their regulation. (4) Finally we consider the relative importance and characteristics of the paracellular route for ion and fluid transfer across epithelia.