Calcium modulation in brain extracellular microenvironment demonstrated with ion-selective micropipette.

Abstract

Changes in extracellular Ca2+ concentration were directly measured in the rat cerebellum, using an ion-selective micropipette. Extracellular K+ was measured simultaneously with a 2nd ion-selective micropipette. The potential reference barrels of the ion electrodes also provided fast field and slow potentials. During repetitive stimulation of the parallel fiber-Purkinje cell cerebellar circuit, extracellular Ca2+ fell to about 80% of base line concentration. During the spreading depression of Leao, extracellular Ca2+ fell to about 10% of base line; decreases of this magnitude also occurred during terminal anoxia. In all cases extracellular K+ increased substantially. Extracellular Ca2+ is apparently modulated during neuronal activity in the CNS, and under some conditions the Ca2+ change can be extreme. Given the well-established and antagonistic effects of reduced extracellular Ca2+ on axonal excitability and synaptic transmission, these results suggest that Ca2+ modulation in the brain cell microenvironment may be a significant parameter in the behavior of neuronal ensembles.