N- and L-Type Voltage-Gated Calcium Channels Mediate Fast Calcium Transients in Axonal Shafts of Mouse Peripheral Nerve

摘要

In the peripheral nervous system (PNS) a vast number of axons are accommodated within fiber bundles that constitute peripheral nerves. A major function of peripheral axons is to propagate action potentials along their length, and hence they are equipped with Na~(+)and K~(+)channels, which ensure successful generation, conduction and termination of each action potential. However little is known about Ca~(2+)ion channels expressed along peripheral axons and their possible functional significance. The goal of the present study was to test whether voltage-gated Ca~(2+)channels (VGCCs) are present along peripheral nerve axons in situ and mediate rapid activity-dependent Ca~(2+)elevations under physiological circumstances. To address this question we used mouse sciatic nerve slices, Ca~(2+)indicator Oregon Green BAPTA-1, and 2-photon Ca~(2+)imaging in fast line scan mode (500 Hz). We report that transient increases in intra-axonal Ca~(2+)concentration take place along peripheral nerve axons in situ when axons are stimulated electrically with single pulses. Furthermore, we show for the first time that Ca~(2+)transients in peripheral nerves are fast, i.e., occur in a millisecond time-domain. Combining Ca~(2+)imaging and pharmacology with specific blockers of different VGCCs subtypes we demonstrate that Ca~(2+)transients in peripheral nerves are mediated mainly by N-type and L-type VGCCs. Discovery of fast Ca~(2+)entry into the axonal shafts through VGCCs in peripheral nerves suggests that Ca~(2+)may be involved in regulation of action potential propagation and/or properties in this system, or mediate neurotransmitter release along peripheral axons as it occurs in the optic nerve and white matter of the central nervous system (CNS).