Ionic transport in the fish gill epithelium

Isolated mitochondria-rich (MR) cells from the rainbow trout gill epithelium were subjected to intracellular pH (pHi) imaging with the pH-sensitive dye BCECF-AM. MR cells were categorized into two distinct functional subtypes based on their ability to recover pHi from an NH4Cl-induced acidification in the absence of Na+. An apparent link between resting pHi and Na+-independent pHi recovery was made. We observed a unique pHi acidification event that was induced by extracellular Na+ addition. This further classified the mixed MR cell population into two functional subtypes: the majority of cells (77%) demonstrated the Na+-induced pHi acidification, whereas the minority (23%) demonstrated an alkalinization of pHi under the same circumstances. The focus of this study was placed on the Na+-induced acidification and pharmacological analysis via the use of amiloride and phenamil, which revealed that Na+ uptake was responsible for the intracellular acidification. Further experiments revealed that pHi acidification could be abolished when Na+ was allowed entry into the cell, but the activity of an electrogenic Na+-HCO3− cotransporter (NBC) was inhibited by DIDS. The electrogenic NBC activity was supported by a DIDS-sensitive, Na+-induced membrane potential depolarization as observed via imaging of the voltage-sensitive dye bis-oxonol. We also demonstrated NBC immunoreactivity via Western blotting and immunohistochemistry in gill tissue. We propose a model for transepithelial Na+ uptake occurring via an apical Na+ channel linked to a basolateral, electrogenic NBC in one subpopulation of MR cells.

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Kinetic studies of ion transport by fish gill epithelium

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1980.238.3.r224 ◽

1980 ◽

Vol 238 (3) ◽

pp. R224-R230 ◽

Cited By ~ 4

Author(s):

D. H. Evans

Keyword(s):

Ion Transport ◽

Kinetic Studies ◽

Gill Epithelium ◽

Fish Gill

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The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste

Physiological Reviews ◽

10.1152/physrev.00050.2003 ◽

2005 ◽

Vol 85 (1) ◽

pp. 97-177 ◽

Cited By ~ 1428

Author(s):

David H. Evans ◽

Peter M. Piermarini ◽

Keith P. Choe

Keyword(s):

Gas Exchange ◽

Molecular Techniques ◽

Ionic Regulation ◽

Gill Epithelium ◽

Acid Base ◽

Renal Epithelia ◽

Fish Gill ◽

Terrestrial Vertebrates ◽

And Control ◽

Endocrine Tissues

The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes. Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates. Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself. The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system. Nevertheless, substantial questions about the evolution of these mechanisms and control remain.

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