Fine localization of low and high calcium dependent ATPase activities in the rat sciatic nerve

We tried to demonstrate the electron microscopic histochemical localization of membrane Ca(2+)-ATPase activity in glutaraldehyde-fixed rat sciatic nerves. Although conventional glutaraldehyde fixatives containing impurities interfered with the reactivity of Ca(2+)-ATPase, this activity was successfully preserved in the tissues fixed with pure glutaraldehyde as well as in those fixed with paraformaldehyde. In unmyelinated nerve fibers, an ATPase activity depending on 10 mM CaCl2 was detected on the whole external surface of Schwann cell plasma membranes. In myelinated fibers, this activity was localized on the surface of Schwann cell outer loops at the paranodal region of Ranvier nodes and on the axonal membrane at the nodal region. Another activity depending on 0.1 mM CaCl2 was demonstrated on the axolemma of unmyelinated fibers. These results indicated that there may be two types of Ca(2+)-ATPase activities showing high and low affinity to calcium ions localized in peripheral nerve systems in a different manner between myelinated and unmyelinated fibers.