Influence of temperature acclimatization on sodium--glucose interactions in the goldfish intestine.

1. Transmural potentials across goldfish intestines in vitro were found to depend on the acclimatization temperature of the fish. At any incubation temperature potentials were lower in fish kept previously at a high temperature, and if the transmural potentials were recorded at incubation temperatures equal to the previous acclimatization temperatures the values remained constant from 8 to 30 degrees C. The glucose-evoked potential was also reduced by previous acclimatization of the fish to a high temperature.2. As the sodium concentration was reduced the steady transmural potential increased and later fell in proportion to the low external sodium concentration, but the glucose-evoked potential fell as soon as the sodium concentration was reduced below 140 mM. Similar changes were seen with intestines taken from fish acclimatized to a high temperature but both the steady-state potential and the transitory glucose-evoked potential were more dependent on the external sodium concentration.3. The maximum glucose-evoked potential depended on the concentration of glucose used and temperature acclimatization had no significant effect on this relation. The steady potential was lower in the presence of glucose at low incubation temperatures but higher at higher incubation temperatures, and the temperature at which glucose ceased to inhibit depended on the previous acclimatization temperature. Glucose also lowered the steady potential, whatever the previous acclimatization temperature, when the external sodium concentration was low.4. The inhibitory effect of glucose on the steady potential of an intestine taken from a 30 degrees -acclimatized fish could be abolished by lowering the external concentration of glucose from 27 to 16 mM.5. Intestines taken from fish acclimatized to 3 degrees C gave variable results.6. It is concluded that sodium moves across the luminal membrane of the goldfish mucosa attached to a carrier which can exist in one of two forms. It is changes in this postulated carrier which serve to stabilize sodium transport at different acclimatization temperatures. Changes in the concentration of this postulated carrier may also occur and function in the regulation of sodium transport, particularly at acclimatization temperatures below 15 degrees C, where the switching of the carrier does not operate.