Regulation of amino acid transport across intestines of goldfish acclimatized to different environmental temperatures.

1. Serosal transfers of valine and threonine were measured using everted sacs of anterior intestine taken from goldfish acclimatized to different temperatures.2. Both valine and threonine were actively transported at incubation temperatures equal to or greater than the previous environmental temperature of the fish. There was also a positive serosal transfer of valine, but not threonine, at incubation temperatures below the previous environmental temperature of the fish.3. The mean stable transmural potentials and amino-acid-evoked potentials depended both on the temperature to which the fish had been acclimatized and on the temperature at which the sacs were incubated.4. There was a linear relation between the transmural potential and the serosal transfer of amino acid, one additional mumole of valine or threonine being transferred/2 hr incubation period for each 3 mV rise in potential. There was a less obvious correlation between the amino-acid-evoked potential and on serosal transfer of amino acid.5. Acclimatization of the goldfish intestine from 8 to 25 degrees C, assessed by changes occurring in the transmural potential and serosal transfer of amino acids, tended to stabilize both parameters, but the compensation in each case was only partial.6. It is possible that the imbalance in transfer of valine-like and threonine-like amino acids, seen at incubation temperatures below the previous acclimatization temperature of the fish, has a special function in initiating the process of acclimatization to the new environmental temperature.