Extracellular calcium activity in the injured spinal cord.

The extracellular concentration of calcium ion was measured in canine spinal cord subsequent to spinal injury. In the control animal, we found that calcium activities changed little independent of electrode placement in the spinal cord, were stable during the 3 h necessary to make injury measurements, and were comparable to other estimates of calcium in the interstitial space. After injury, calcium activities decreased to micromolar levels that were incompatible with neural function. An incomplete recovery of extracellular calcium occurred during the next 3 h to about one-third (0.44 +/- 0.01 mM) of the normal value (1.1 +/- 0.08 mM). Such a pattern of changes in extracellular calcium was specific for the injury site itself and did not occur at nearby anatomic loci. These results are interpreted as having both short- and long-term effects on neuronal function and subsequent reorganization of spinal pathways.