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

Abstract

1. 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 degrees C before the experimental incubation at 38 degrees C.2. During incubation at 38 degrees 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 0.5-1.0 mM-methacholine. Similar results were obtained whether the medium contained 10 mM-Tris (used in most experiments) or 25 mM-HCO(3) (-) 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(-), NO(3) (-) or SO(4) (2-), 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 Cl(-) 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 Na(+) 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 SO(4) (2-). The effects of methacholine were partially blocked when NO(3) (-) replaced Cl(-).7. The results are consistent with the stimulation by methacholine of a furosemide-sensitive, 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.