Calcium modulation in brain extracellular microenvironment demonstrated with ion-selective micropipette.
Changes in extracellular Ca2+ concentration were directly measured in the rat cerebellum, using an ion-selective micropipette. Extracellular K+ was measured simultaneously with a second 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 Leão, 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. These results show that extracellular Ca2+ is modulated during neuronal activity in the central nervous system and that under some conditions the Ca2+ change can be extreme. Given the well-established and antagonistic effects of reduce 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.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002531:Cerebellum / Q000378:metabolism*; D013181:Cortical Spreading Depression; D004558:Electric Stimulation; D005110:Extracellular Space / Q000378:metabolism*; D000860:Hypoxia / Q000378:metabolism; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology; D011188:Potassium / Q000378:metabolism; D011689:Purkinje Cells / Q000502:physiology; D051381:Rats
D011188:Potassium; D002118:Calcium
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