| Summary: | The rectal gland of the spiny dogfish, Squalus acanthias, provides an easily studied model of active chloride transport powered indirectly by Na-K-ATPase. Co-transport of sodium with chloride can be demonstrated in membrane vesicles isolated from basolateral membranes of the gland. Chloride secretion is under the hormonal control of vasoactive intestinal peptide, and possibly other agents, via adenyl cyclase and cyclic AMP. A similar mechanism is probably responsible for the active transport of chloride across other biological membranes. Thirty years ago, when James Gamble summarized the facts of water and electrolytes for an admiring generation of medical students, the transport of chloride was considered to be entirely passive. Excluded from cells, chloride was regarded as a kind of filler, its movement dependent entirely upon the varied whims of sodium, potassium, and bicarbonate. Gamble epitomized this notion of chloride by calling it "a mendicant ion." It is becoming apparent that far from being a mendicant ion, chloride is in fact actively transported by a number of animal tissues, including the central nervous system, and especially by secretory epithelial organs. It has been the study of the
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