Does Endogenous Norepinephrine Regulate Potassium Homeostasis and Metabolism in Rat Cerebral Cortex?

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Abstract
The role of endogenous cerebral norepinephrine (NE) as a modulator of transmembrane cation transport and energy metabolism was evaluated by monitoring extracellular potassium ion activity ([K+]o) in vivo and by measuring cortical Na+,K+-ATPase activity and oxygen consumption in vitro, Ipsilateral cortical NE was depleted by unilateral 6-hydroxydopamine (6-OHDA) lesions of the locus ceruleus (LC). The contralateral cortex was used for control measurements. NE depletion had no effect on resting levels of cortical [K+]o or on the rate of K+removal from the extracellular space following direct cortical stimulation. There was also no effect of NE depletion on Na+,K+-ATPase activity in cortical homogenates nor on oxygen consumption of cortical slices over a wide range of K+concentrations. These results indicate that central NE depletion does not influence movements of cortical K+either directly through an influence on Na+,K+-ATPase activity or indirectly through effects on oxidative metabolism. It is probable, therefore, that previously described effects of NE on cortical oxidative metabolism are mediated through changes in cerebral perfusion and/or modification of substrate availability in vivo.