Intracellular free calcium concentration in transected spinal axons
Abstract
An increase in intracellular free calcium concentration ($\rm\lbrack Ca\sp{2+}\rbrack\sb{i}$) has been implicated in the degeneration of transected axons. We used fura-2 to measure the $\rm\lbrack Ca\sp{2+}\rbrack\sb{i}$ in the last few mm of the proximal segments of transected spinal axons. There is a spatially graded increase in $\rm\lbrack Ca\sp{2+}\rbrack\sb{i}$ that is complete within minutes; at 0.5 mm from the cut end, the $\rm\lbrack Ca\sp{2+}\rbrack\sb{i}$ is 14 times greater than basal levels and at two mm, it is three times greater. Superimposed on this initial change is a moving front of calcium that progresses up the axon, reaching 1.6 mm from the cut end in three hours. In these regions, $\rm\lbrack Ca\sp{2+}\rbrack\sb{i}$ exceeds what can be reliably measured with fura-2 (10 $\mu$M). One day after transection, $\rm\lbrack Ca\sp{2+}\rbrack\sb{i}$ returns to precut levels except in the distal 300 $\mu$m indicating that the high levels of $\rm\lbrack Ca\sp{2+}\rbrack\sb{i}$ do not result in the immediate destruction of the axon. The application of a DC electric field decreases or increases, depending on polarity, the penetration of the front of $\rm Ca\sp{2+}$ into the axon. All of these changes in $\rm\lbrack Ca\sp{2+}\rbrack\sb{i}$ that occur following transection require extracellular calcium.
Degree
Ph.D.
Advisors
Robinson, Purdue University.
Subject Area
Biology
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