Uptake of L‐ and D‐alanine by a brackish‐water Bivalve, Corbicula japonica, with special reference to their transport pathways and the salinity effect

Abstract

The uptake of L-and D-alanine by intact animals or isolated gills of a brackishwater bivalve, Corbicula japonica, was investigated in relation to their transport pathways and the possible physiological roles. The animals took up L-alanine a t concentrations as low as 10 FM. Both the net transport and the influx were strongly affected by external salinity; animals acclimated to fresh water showed much lower rates of net transport and influx than did animals acclimated to 250 mOsm. Patterns of accumulation of 14C-L-alanine in different tissues of intact animals revealed that the gill was the principal site for the transport of the amino acid. Influx of both l4C-L-and 14C-D-alanine into isolated gills was inhibited by a-neutral amino acids, but not by a-acidic or p-amino acids; all a-neutral amino acids examined (glycine, L-glutamine, L-leucine, L-valine, and even D-and L-alanine) inhibited the influx of D-alanine more strongly than the influx of L-alanine. Kinetic analysis of the influx indicated that D-and L-alanine were transported via the same carrier(s1, but that the carrier(s) had a higher affinity for L-alanine than for D-alanine. The transport mechanism appears to play a significant role in the net uptake of D-and L-alanine or in the re-uptake of the amino acids diffused from the integument according to the ambient concentrations of the substrates. o 1992 Wiley-Liss, Inc.

Distribution of Free D-Amino Acids in Bivalve Mollusks and the Effects of Physiological Conditions on the Levels of D- and L-Alanine in the Tissues of the Hard Clam, <i>Meretrix lusoria</i>

“…[1][2][3][4][5][6][7][8] Even the distribution of these D-amino acids, however, is still con troversial on various molluscan species. It is not clear whether the distribution of D-amino acids depends on the phylogenetic positions or ecological environments.…”

Purification and some properties of alanine racemase from the marine gastropod Cellana grata

“…The occurrence of alanine racemase, which is involved in the synthesis of d ‐alanine in the C. grata tissues, indicates that d ‐alanine plays some positive physiological roles. It is thought that d ‐alanine functions as an osmolyte in some invertebrates 7–9 . C. grata , however, inhabits near the top of the intertidal zone and remains out of water for long time intervals.…”

“…d ‐Amino acids are reported to occur in various animals 1–3 . In many aquatic invertebrates, free d ‐alanine is widely found in several tissues 4–7 where it serves as the principal osmolyte in the regulation of intracellular osmolarity 7–9 . In Corbicula japonica , a brackish water bivalve, d ‐ and l ‐alanine are the major osmolytes in the intracellular free amino acid pool, and their intracellular levels fluctuate in response to the changes in external salinity, thereby maintaining a constant level of d ‐/ l ‐alanine 7,8 .…”

“…[1][2][3] In many aquatic invertebrates, free Dalanine is widely found in several tissues [4][5][6][7] where it serves as the principal osmolyte in the regulation of intracellular osmolarity. [7][8][9] In Corbicula japonica, a brackish water bivalve, D-and L-alanine are the major osmolytes in the intracellular free amino acid pool, and their intracellular levels fluctuate in response to the changes in external salinity, thereby maintaining a constant level of D-/Lalanine. 7,8 In response to acclimation of freshwater crayfish Procambarus clarkii to seawater, free Dalanine accumulates in the muscles of the crayfish, and under these conditions, the concentration of free D-alanine increases to more than 30-fold.…”

“…[7][8][9] In Corbicula japonica, a brackish water bivalve, D-and L-alanine are the major osmolytes in the intracellular free amino acid pool, and their intracellular levels fluctuate in response to the changes in external salinity, thereby maintaining a constant level of D-/Lalanine. 7,8 In response to acclimation of freshwater crayfish Procambarus clarkii to seawater, free Dalanine accumulates in the muscles of the crayfish, and under these conditions, the concentration of free D-alanine increases to more than 30-fold. 9 These observations suggest that D-alanine acts as an osmolyte in the regulation of cell volume.…”