Ions and energy metabolism in duck salt‐gland: possible role of furosemide‐sensitive co‐transport of sodium and chloride

Abstract

SUMMARY1. The effects of methacholine on net ionic movements and energy metabolism of the avian salt-gland have been studied, using slices of glands taken from salt-adapted Pekin ducks. The slices were equilibrated with media and drugs for 120 min at 1 0C before the experimental incubation at 38 'C.2. During incubation at 38 'C the slices accumulated K+ and lost Na+ and Cl-. In the presence of methacholine, they retained more Na+ and Cl-and accumulated less K+, the maximal effects being given by 05-1 0 mM-methacholine. Similar results were obtained whether the medium contained 10 mM-Tris (used in most experiments) or 25 mM-HC03-as the major buffer.3. The higher final levels of cell Na+ and Cl-induced by methacholine were not seen when furosemide (1 mM) was also present. Methacholine did not induce a higher level of cell Na+ when medium Cl-was replaced by I-, NO3-or S042-, and did not induce a higher Cl-content when medium Na+ was replaced by choline or Li+. The fall of K+ accumulation caused by methacholine was also prevented by furosemide or by replacing C1-in the medium with other anions. The anion-transport inhibitors, SCN-(up to 10 mM) and 4,4'-diisothiocyano-2,2'-disulphonic acid stilbene (DIDS) (up to 2 mM) did not prevent the effects of methacholine.4. Methacholine stimulated respiration and lowered the slice ATP contents, and these effects were both prevented by ouabain or furosemide. Ouabain, but not furosemide, also reduced the basal (i.e. in the absence of methacholine) rate of respiration and raised the ATP level. SCN-and DIDS had no effect on basal or stimulated respiration or on ATP contents.5. The respiratory stimulation and fall of ATP induced by methacholine were totally prevented if medium Na+ was replaced by choline. Replacement of Nat by Li+ caused some stimulation of basal respiration; it also permitted some loss of ATP in the presence of methacholine, but the loss was smaller than that seen in the normal Na+ medium.6. The respiratory stimulation and fall of ATP induced by methacholine were prevented if medium Cl-was replaced by S042-. The effects of methacholine were partially blocked when N03-replaced Cl-. S. A. ERNST AND G. D. V. VAN ROSSUM 7. The results are consistent with the stimulation by methacholine of a furosemidesensitive, coupled entry of Na+ and Cl-into the cells, associated with a loss of K+. This would result in a stimulation of Na+ extrusion by the ouabain-sensitive transport system for Na+ and K+ with increased consumption of ATP.

Plasma membrane biogenesis in the avian salt gland: A biochemical and quantitative electron microscopic autoradiographic study

“…It is unclear why an increase in RNA synthesis could not be detected under in vitro conditions, since previous studies indicate that total RNA content of the salt gland increases following saIt stress (Holmes and Stewart, 1968). Although some cellular metabolic activities of the salt gland may require continuous cholinergic stimulation (Stewart et al, 1979;Stewart and Sen, 1981;Ernst and Van Rossum, 1982), we found no effect by cholinergic agonists on in uitro RNA synthetic rates in either nonstressed or stressed salt-gland slices (data not shown). In contrast to the in vitro studies, however, the in vivo rates found in the present study are consistent with earlier observations and appear to reflect true biosynthetic events.…”

Effects of ouabain on potassium transport and cell volume regulation in rat and rabbit liver.

“…3). A similar delay of net K+ uptake is also seen in rat liver slices (Judah & McLean, 1962;Elshove & van Rossum, 1963;van Rossum, 1970b) but not in rat renal cortex, rat lung or avian salt gland (Ernst & van Rossum, 1982;Russo et al 1985; M. F. Mariani & G. D. V. van Rossum, unpublished). Intracellular Na+ initially followed a similar course to water and Cl-but, unlike the latter, continued to decline after 30 min.…”

Salt Gland Function in the Green Sea Turtle Chelonia Mydas

“…The concentration mechanism employed by chelonian salt glands is unknown. In birds there is evidence of transepithelial Cl~ secretion (Ernst & van Rossum, 1982), although the initial fluid at the blind end of the salt gland tubules appears to be isotonic with blood (Marshall etal. 1985), and it is suggested that the fluid is concentrated, as it passes along the duct, by water absorption across the duct wall under the influence of a standing osmotic gradient, and that further ionic modifications in the fluid composition are brought about by ion pumps (Ellis et al 1977;Marshall et al 1985).…”