Overview of epithelial ion-transport mechanisms

Abstract

SHUTTLEWORTH, T. J. 1989. Overview of epithelial ion-transport mechanisms. Can. J. Zool. 67: 3032-3038.The basic cellular transport mechanisms for the transepithelial uptake and elimination of sodium and chloride ions are briefly reviewed. These frequently involve processes defined as secondary active mechanisms, and the problems that this creates for their identification in epithelial systems are emphasised. It is suggested that despite the wide range of epithelial tissues involved in body fluid ion regulation, current evidence indicates that a relatively limited group of these secondary active carriers is involved in the transport process, and the basis for this evolutionary conservatism is discussed, together with certain of its implications. Finally, the interactions of the transport mechanisms with metabolic and acid-base parameters are contrasted in ion-uptake and ion-excretion situations, and the possible roles of carbonic anhydrase compared. SHUTTLEWORTH, T. J. 1989. Overview of epithelial ion-transport mechanisms. Can. J. Zool. 67 : 3032-3038.Les mCcanismes de base qui assurent le transport transCpithClia1 dans les cellules lors de l'absorption et de 1'Climination des ions sodium et des ions chlorure sont rCvisCs brikvement. Ces mCcanismes impliquent souvent des processus dCfinis comme des mCcanismes actifs secondaires et les problCmes que cela entrafne dans l'identification des systkmes CpithCliaux sont exposks. I1 semble qu'en dCpit de la grande variCtC de tissus CpithCliaux en cause dans la rCgulation ionique des fluides du corps, les travaux rCcents indiquent qu'un groupe relativement restreint de ces transporteurs secondaires actifs jouent un r61e dans le processus de transport. La raison de ce conservatisme Cvolutif et certaines de ses consCquences font l'objet d'une discussion. Enfin, les interactions entre, d'une part, les mCcanismes de transport et, d'autre part, les variables mCtaboliques et les variables qui jouent un r61e dans 1'Cquilibre acide -base, sont comparCes dans des conditions d'absorption et des conditions d'excrCtion d'ions; les r6les probables de l'anhydrase carbonique sont examinks.[Traduit par la revue] IntroductionThe purpose of this brief review is not to attempt to describe in detail all the different mechanisms of ion transport across animal cell me~nbranes, but to outline some current models describing the epithelial uptake and elimination of the principal ions of vertebrate animal body fluids, sodium and chloride, and to consider some of their implications. Particular attention will be paid to a discussion of certain consequences of the fact that these transport models frequently involve processes defined as secondary active mechanisms, and of the possible interactions of these ion-regulating systems with important metabolic and acid -base parameters.

Localization of mRNA for the proton pump (H+-ATPase) and exchanger in the rainbow trout gill

“…Previous studies have suggested that the proton pump is associated specifically with the chloride cell (Lin and Randall 1991), the pavement cell (Laurent et al 1994;Sullivan et al 1995), or both (Lin et al 1994;Lin and Randall 1995). Considerable indirect evidence suggests that C1-uptake is achieved by a Band 3 or Band 3-like C1-IHC05 exchanger located on the apical membrane of chloride cells (reviewed by McDonald et al (1989) ;Shuttleworth 1989;Avella and Bornancin 1990;Perry and Laurent 1993;Evans 1993;Marshall 1995). The existence of the C1-IHCO: exchange mechanism in the fish gill and its association with chloride cells is based exclusively on correlative studies linking chloride cell fractional surface area to the rates of C1-uptake (Perry and Laurent 1989;Laurent and Perry 1990;Perry et al 1992) or branchial net acid equivalent excretion (Goss et al 1992a(Goss et al , 1994aGoss and Perry 1994;Perry and Goss 1994).…”

In vivo bafilomycin-sensitive Na+ uptake in young freshwater fish

“…Freshwater teleosts absorb Na+ from the ambient medium against steep concentration gradients (Maetz and Garcia-Romeu, 1964; for a review, see Perry, 1997). This uptake was originally attributed to an electroneutral Na+/H+ (or NFU*) antiporter (Krogh, 1938) located in the apical membrane of the branchial epithelium (Wright and Wood, 1985;Shuttleworth, 1989; for a review, see Marshall, 1995). But several substantive observations led to this paradigm being abandoned.…”