Action de la vératrine, de la cocaïne et de la stimulation électrique sur la synthèse et sur le pool des acides aminés de la chaîne nerveuse ventrale du homard

Abstract

Resume 1. 1. The synthesis of amino acids from [ 14 G 6 ]glucose and [I- 14 C]pyruvate in the ventral nerve cord of the lobster ( Homarus vulgaris L.) has beeb studied under the following conditions: in the presence of veratrine sulfate (4 μM), cocaine hydrochloride (4 mM) and during electrical stimulation. Our results show that veratrine and electrical stimulation increase the turn-over rate of the following amino acids: alanine, glycine, glutamic acid and aspartic acid. Cocaine brings about a decrease in the turn-over rate of dicarboxylic acids (glutamic acid and aspartic acid) and an increase in the labelling of alanine and glycine. Our experimental conditions are without effect on the labelling of arginine and lysine. These results are discussed in the light of the various metabolic pathways envisaged in a previous paper. Veratrine and electrical stimulation seem to be without effect on the rate of pyruvate amination. On the contrary, they seem to affect the metabolic pathways involving hydroxypyruvate or the decarboxylation in C-1 of pyruvate. Moreover, it would appear that these experimental conditions increase the rate of entry of pyruvate into the Krebs cycle. Concerning the effects of cocaine, our results indicate that it inhibits the access of pyruvate to the Krebs cycle. 2. 2. Contrary to that observed with cocaine, veratrine sulfate and electrical stimulation affect the cationic composition of the nerve cord (increase in Na concentration, decrease in K concentration). 3. 3. The pool of intracellular free amino acids is unaffected by veratrine. Thus veratrine seems to increase the turn-over rate of various amino acids. This conclusion is substantiated by the fact that the ammoniac content increases after application of veratrine. Electrical stimulation leads to an increase in the total concentration of the pool of free amino acids. 4. 4. The results are discussed within the framework of the osmoregulatory phenomena in aquatic invertebrates. A hypothesis concerning the mechanisms used by euryhaline invertebrates to adjust the intracellular concentration to that of the internal medium is proposed.