Action potentials induce uniform calcium influx in mammalian myelinated optic nerves.
The myelin sheath enables saltatory conduction by demarcating the axon into a narrow nodal region for excitation and an extended, insulated internodal region for efficient spread of passive current. This anatomical demarcation produces a dramatic heterogeneity in ionic fluxes during excitation, a classical example being the restriction of Na influx at the node. Recent studies have revealed that action potentials also induce calcium influx into myelinated axons of mammalian optic nerves. Does calcium influx in myelinated axons show spatial heterogeneity during nerve excitation? To address this, we analyzed spatial profiles of axonal calcium transients during action potentials by selectively staining axons with calcium indicators and subjected the data to theoretical analysis with parameters for axial calcium diffusion empirically determined using photolysis of caged compounds. The results show surprisingly that during action potentials, calcium influx occurs uniformly along an axon of a fully myelinated mouse optic nerve.
Zhang
Chuan-Li
CL
Dept. of Physiology, University of Wisconsin School of Medicine, 1300 University Ave., 277 Medical Science Bldg., Madison, WI 53706, USA.
Wilson
J Adam
JA
Williams
Justin
J
Chiu
Shing Yan
SY
D000200:Action Potentials / Q000502:physiology*; D000465:Algorithms; D000818:Animals; D001369:Axons / Q000378:metabolism; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology; D017610:Calcium Compounds; D020013:Calcium Signaling / Q000502:physiology*; D003198:Computer Simulation; D004058:Diffusion; D004594:Electrophysiology; D066298:In Vitro Techniques; D051379:Mice; D018613:Microscopy, Confocal; D008959:Models, Neurological; D009186:Myelin Sheath / Q000502:physiology*; D009900:Optic Nerve / Q000166:cytology / Q000378:metabolism*; D010782:Photolysis; D012964:Sodium / Q000502:physiology
D020746:Calcium Channels, L-Type; D017610:Calcium Compounds; D002104:Cadmium; D012964:Sodium; D002118:Calcium