Characterization of the norepinephrine-activation of adenylate cyclase suggests a role in memory affirmation pathways: Overexposure to epinephrine inactivates adenylate cyclase, a causal pathway for stress-pathologies

Abstract

Incubation with noradrenaline (norepinephrine) of isolated membranes of rat's brain corpus striatum and cortex, showed that ionic-magnesium (Mg 2+) is required for the neurotransmitter activatory response of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing) (EC 4.6.1.1)], AC. An Mg 2+-dependent response to the activatory effects of adrenaline, and subsequent inhibition by calcium, suggest capability for a turnover, associated with cyclic changes in membrane potential and participation in a short-term memory pathway. In the cell, the neurotransmitter by activating AC generates intracellular cyclic AMP. Calcium entrance in the cell inhibits the enzyme. The increment of cyclic AMP activates kinase A and their protein phosphorylating activity, allowing a long-term memory pathway. Hence, consolidating neuronal circuits, related to emotional learning and memory affirmation. The activatory effect relates to an enzyme–noradrenaline complex which may participate in the physiology of the fight or flight response, by prolonged exposure. However, the persistence of an unstable enzyme complex turns the enzyme inactive. Effect concordant, with the observation that prolonged exposure to adrenaline, participates in the etiology of stress triggered pathologies. At the cell physiological level AC responsiveness to hormones could be modulated by the concentration of chelating metabolites. These ones produce the release of free ATP 4−, a negative modulator of AC and the Mg 2+ activated insulin receptor tyrosine kinase (IRTK), thus, allowing an integration of the hormonal response of both enzymes by ionic controls. This effect could supersede the metabolic feedback control by energy charge. Accordingly, maximum hormonal response of both enzymes, to high Mg 2+ and low free ATP 4−, allows a correlation with the known effects of low caloric intake increasing average life expectancy.