Transport Characteristics of the Colonic Epithelium of the Japanese Quail ( Coturnix coturnix)

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 μmoles/g), an intermediate level of salt intake. Experiments were performed on unstripped colons in standard Ussing chambers with bicarbonate/CO 2 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 μA/cm 2) were lower than those reported for chickens on a similar diet, whereas tissue resistance (76.06 ± 4.19 Ω·cm 2) was similar. Addition of amino acids (4 mM leucine + lysine) increased SCC by 10.85 ± 1.97 μA/cm 2. Both phloridzin (1 mM) and amiloride (10 −5M) decreased SCC, by 7.05 ± 1.26 and 9.64 ± 2.68 μA/cm 2, 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 μg/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.