Abstract

The colon of the domestic fowl sustains a reabsorptive Na+ current on both high- and low-sodium diets. However, there is a marked shift in the apical transport step under these two extreme conditions, from amino acid/hexose cotransport on high-salt diets to amiloride-sensitive Na+ channels on low-salt diets. The present experiments were performed to study colonic Na+ transport in another galliform species, the Japanese quail (Coturnix coturnix). Birds were maintained on a commercial game feed containing 0.18% Na+ (78 mumoles/g), an intermediate level of salt intake. Experiments were performed on unstripped colons in standard Ussing chambers with bicarbonate/CO2 buffer solution on both sides. Baseline values (n = 11) for PD (3.13 +/- 0.68 mV) and short circuit current (SCC, 30.87 +/- 7.79 microA/cm2) were lower than those reported for chickens on a similar diet, whereas tissue resistance (76.06 +/- 4.19 omega.cm2) was similar. Addition of amino acids (4 mM leucine + lysine) increased SCC by 10.85 +/- 1.97 microA/cm2. Both phloridzin (1 mM) and amiloride (10(-5) M) decreased SCC, by 7.05 +/- 1.26 and 9.64 +/- 2.68 microA/cm2, respectively. Thus, on this diet the quail colonic epithelium maintains both amino acid/hexose cotransporter activity and amiloride sensitive channel activity. Arginine vasotocin (10(-6) M) caused a small, but consistent decrease in SCC, while acetazolamide increased SCC. Aldosterone (128 micrograms/kg), given 4 hr prior to the experiment (n = 4) significantly reduced the amino acid stimulated SCC. These results confirm, for the Japanese quail, the presence of multiple apical Na+ entry mechanisms in colonic epithelium. Amino acid cotransporter activity, in particular, appears to be highly sensitive to aldosterone suppression.