Stimulus-induced changes in extracellular Na super(+) and Cl super(-) concentration in relation to changes in the size of the extracellular space

• Published in: Experimental brain research 1982-01, Vol.46 (1), p.73-84
• Main Authors: Dietzel, I, Heinemann, U, Hofmeier, G, Lux, H D
• Format: Article
• Language: English
• ISSN: 0014-4819

Extracellular Na super(+)- and Cl super(-)-concentrations ((Na super(+)) sub(o), (Cl super(-)) sub(o)) were recorded with ion-selective microelectrodes during repetitive stimulation and stimulus-induced self-sustained neuronal afterdischarges (SAD) in the sensorimotor cortex of cats. In all cortical layers (Na super(+)) sub(o) initially decreased by 4-7 mM. In depths of more than 600 mu m below the cortical surface such decreases usually turned into increases of 2-6 mM during the course of the SADs, whereas in superficial layers (Na super(+)) sub(o) never rose above its resting level. (Cl super(-)) sub(o) always showed an increase in the course of the SADs often preceded by an initial small decrease. The average increase at a depth of 1,000 mu m was about 7 mM. (Cl super(-)) sub(o) reached peak values at about the end of the ictal period, whereas (Na super(+)) sub(o) reached its maximum shortly after the end of the SAD, at times when (K super(+)) sub(o) was still elevated above the baseline concentration. These data indicate that the extracellular osmolarity can increase during SAD by up to 30 mM. Such an increase in osmolarity can be explained by an increase in the number of intracellular particles, caused by cleavage of larger molecules during enhanced metabolism. This could lead to cell-swelling due to passive water influx from the extracellular space (ES).