Amino acid transport in the intestinal mucosa of temperature-acclimated carp

Abstract

The effects of temperature and photoperiod acclimation of carp upon the villus distribution and activity of amino acid transport systems on intestinal villi has been determined. Unindirectional apical influx of alanine, in the presence and absence of Na +, and of lysine in the presence of Na +, was restricted to the distal part of the villus. Alanine influx (Na +-dependent) at 20°C was substantially greater in villi of 10°C-acclimated carp compared to 30°C-acclimited carp at all positions on the villus, and the length of villus over which transport was observed was significantly greater. This resulted ina doubling of villus transport capacity for alanine on cold-acclimition by means of both an increased transporting area and a greater area-specific transport activity of cold-acclimated enterocytes. Na +-independent alanine influx was small compared, to the Na +-dependent mechanism but was also greater in cold-acclimated fish. By contrast, Na +-dependent lysine influx was greater in the villi of 30°C-acclimated carp relative to 10°C-acclimated carp although there was no difference in the length of villus over which transport was detected. These contrasting acclimation responses of the Na +-dependent alanine and lysine transport mechanisms show that the straightforward compensatory interpretation for transport processes does not apply. Instead, it is suggested that Na +-dependent lysine and alanine carriers are expressed independently with time-courses which are differently affected by cooling. Differences in the maturity of the transporting population of enterocytes in cold- and warm-acclimated carp may lead to the elaboration of transport systems to differing extents.