Supralinear Ca2+ signaling by cooperative and mobile Ca2+ buffering in Purkinje neurons.
Endogenous high-affinity Ca2+ buffering and its roles were investigated in mouse cerebellar Purkinje cells with the use of a low-affinity Ca2+ indicator and a high-affinity caged Ca2+ compound. Increases in the cytosolic Ca2+ concentration ([Ca2+]i) were markedly facilitated during repetitive depolarization, resulting in the generation of steep micromolar Ca2+ gradients along dendrites. Such supralinear Ca2+ responses were attributed to the saturation of a large concentration (0.36 mM) of a mobile, high-affinity (dissociation constant, 0.37 microM) Ca2+ buffer with cooperative Ca2+ binding sites, resembling calbindin-D28K, and to an immobile, low-affinity Ca2+ buffer. These data suggest that the high-affinity Ca2+ buffer operates as the neuronal computational element that enables efficient coincidence detection of the Ca2+ signal and that facilitates spatiotemporal integration of the Ca2+ signal at submicromolar [Ca2+]i.
Maeda
H
H
Department of Physiology, Faculty of Medicine, University of Tokyo, Japan.
Ellis-Davies
G C
GC
Ito
K
K
Miyashita
Y
Y
Kasai
H
H
D000465:Algorithms; D000818:Animals; D002021:Buffers; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology; D004396:Coloring Agents; D004533:Egtazic Acid / Q000031:analogs & derivatives; D004594:Electrophysiology; D005456:Fluorescent Dyes; D016257:Fura-2; D051379:Mice; D017711:Nonlinear Dynamics; D010782:Photolysis; D011690:Purkinje Fibers / Q000502:physiology*
D002021:Buffers; D004396:Coloring Agents; D005456:Fluorescent Dyes; C117677:dimethoxynitrophenyl-EGTA-4; D004533:Egtazic Acid; D002118:Calcium; D016257:Fura-2