ISSN:
1432-1351
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary Ca in desheathed trunks of sciatic nerve ofRana pipiens is completely exchangeable with radioactive45Ca.45Ca distributes in three compartments, one intracellular compartment and two extracellular compartments, which exchange Ca with greatly different rate coefficients. Using impermeable solutes (sucrose, inulin, SO4) and electron microprobe techniques, we have identified the rapidly exchanging extracellular compartment as the interstitial space and the slowly exchanging extracellular compartment, accessible to solutes up to a molecular weight of 5,500, as the mesaxonal gap in the myelin sheath. Ca exists in both extracellular compartments as free Ca and in bound form. After equilibration in solutions containing 1 mM Ca, the contents of the extracellular compartments in mmole/kg wet weight are: 1) Interstitial space: free Ca=0.52, bound Ca=0.19; 2) Myelin region: free Ca=0.12, bound Ca 0.27. The intracellular space contains 0.11 mmole/kg wet weight of Ca. After 4 h of washout,45Ca release represents the Ca flux from the intracellular compartment since it can be inhibited 95% by the combined action of Na and Ca removal and the addition of La. Our results suggest further that45Ca release after this time represents a close approximation of the Ca transport across the axolemmal membrane.45Ca, therefore, represents a suitable tracer probe to investigate Ca compartmentalization and Ca exchange in this tissue.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00609934
