Glucsoe and amino acidmetabolism in octopus optic and vertical lobes in vitro.

Abstract

Abstract—(1) The metabolism of glucose and amino acids in vitro was compared in the rat cerebral cortex and the optic and vertical lobes of the octopus brain.(2) Specific activities and pool sizes of the five amino acids, glutamate, aspartate, glutamine, alanine and γ‐aminobutyric acid (GABA), were determined in octopus and rat brain slices after 2 hr incubation with 10 mm‐[U‐14C]glucose, 10 mm‐L‐[U‐14C]glutamate, and 10mm‐L‐[U‐14C]glutamate with added 10 mM‐glucose. Amino acid pool sizes were similar in rat and octopus brain, with the exception of alanine, which was higher in the octopus. Generally specific activities were from four‐ to 20‐fold higher in rat brain. With [U‐14C]glucose as substrate, specific activities of GABA and glutamate were highest in rat; those of alanine and glutamine highest in octopus brain. With L‐[U‐14C]glutamate the specific activities of GABA and aspartate were highest in rat, that of aspartate highest and GABA lowest in octopus. The addition of glucose to L‐[U‐14C]glutamate as substrate had little effect on the specific activities of any of the amino acids.(3) The uptake of some amino acids was determined by incubation with [U‐14C]amino acids for 2 hr, and 14CO2 formation was also measured. The amount of label taken up by octopus was uniformly 20‐25 per cent of that found for rat brain. The amount of 14CO2, however, differed according to the amino acid. Four times as much 14CO2 was generated from alanine by octopus optic lobe and twice as much by the vertical lobe than rat cortex, but from glutamate, only 24 per cent in the optic and 15 per cent in the vertical lobe. No 14CO2 was generated from [U‐14C]GABA in the octopus, by contrast with the rat.(4) Activity of some of the enzymes involved in amino acid metabolism was determined in homogenates of rat cortex and octopus optic and vertical lobes, with and without activation by Triton X‐100. Enzymic activities in the octopus, with the exception of alanine aminotransferase, were lower than in the rat, and glutamate decarboxylase could not be detected in octopus brain, in the absence of detergent.