Enzyme reaction rate studies in electromotor neurons of the weakly electric fishApteronotus leptorhynchus

Abstract

A histochemical analysis of reaction rates of a series of enzymes was performed in electromotor neurons of the weakly electric fish Apteronotus leptorhynchus. These neurons were selected because of their functional homogeneity. The high metabolic activity of these cells as well as their large size facilitate cytophotometric analysis in cryostat sections. Sections were incubated for the activity of hexokinase, glucose-6-phosphate dehydrogenase, succinate dehydrogenase, NADPH dehydrogenase, NADPH ferrihaemoprotein reductase and beta-hydroxybutyrate dehydrogenase. All media contained polyvinyl alcohol as tissue stabilizer and Nitro BT as final electron acceptor. Measurements were performed with a Vickers M85a cytophotometer. Linear relationships between the specific formation of formazan (test minus control reaction) and incubation time were obtained for all enzymes although some reactions showed an initial lag phase or an intercept with the ordinate. The relatively high activities of hexokinase, succinate dehydrogenase and the extremely low activity of hydroxybutyrate dehydrogenase indicate that energy is mainly supplied by glycolysis. Glucose-6-phosphate dehydrogenase showed a high activity whereas NADPH reductase and dehydrogenase activity were low in electromotor neurons, indicating that the NADPH generated is largely used for biosynthesis. Despite their synchronous firing pattern activity, electromotor neurons showed a considerable heterogeneity with respect to their metabolic activity.

Histochemical Demonstration of the Alterations in the Renal Dehydrogenases Activities Induced by Lead in Wistar Albino Rats (Rattus norvegicus).

“…Phenazine methosulphate, an intermediate electron acceptor was added to the incubating media of the soluble dehydrogenases in the rate of 1 mg/ml of the medium. 23,24) The activities of the soluble nicotinamide adenine dinucleotide-dependent dehydrogenases were demonstrated by means of the optimizid polyvinyl alcohol technique, 25) where 2 ml of 20 per cent polyvinyl alcohol were mixed with 2 ml of incubation medium of the dehydrogenases.…”

“…Sections were incubated at 37°C for 15 min, post-treated in 4 per cent formaldehyde and mounted in glycerine jelly. NADPH Dehydrogenase ---The reaction of this reductase was performed by the method of Pearse as modified by Straatsburg et al 24) The final incubating medium consisted of 9 ml NBT tetrazolium stock solution, 1 ml distilled water, 2 mg NADPH and 0.1 ml menadione (1 mM). Sections were incubated at 37°C for 10 min, post-treated in 4 per cent formaldehyde and mounted in glycerine jelly.…”

Effects of chemical contaminants on the health of Mytilus edulis from Puget Sound, Washington. II. Cytochemical detection of subcellular changes in digestive cells

“…NADPH-ferrihaemoprotein reductase activity in the mussel digestive cells was very low in the absence of substrate (negative control) in the reaction medium (Table 1). The cytochemical detection of DTD was carried out as described by Straatsburg et al (1989). Incubation medium and procedures were identical to those for NFR activity, save only that NADH was substituted fo r NADPH.…”