Spatial heterogeneity of intracellular Ca2+ signals in axons of basket cells from rat cerebellar slices.
1. Using tight-seal whole-cell recording and digital fluorescence imaging, we studied intracellular calcium (Ca2+i) dynamics in cerebellar basket cells, whose dendrites, axon and presynaptic terminals are coplanar, an optimal configuration for simultaneous optical measurements of all functional domains. 2. In Cs(+)-loaded neurones, depolarizing pulses induced large Ca2+i transients in single axonal varicosities and synaptic terminals, contrasting with much weaker signals between varicosities or in the somato-dendritic domain. 3. Axonal branch points consistently displayed [Ca2+]i rises of similar magnitude and time course to those in axonal terminals and varicosities. 4. In biocytin-filled basket cells, varicosity-like swellings were present along the axon including its branch points. Thus, axonal enlargements are not due to fluorescence-induced cell damage. 5. The spatial heterogeneity of Ca2+i signals was also observed in K(+)-loaded cells upon depolarizing trains, suggesting that this behaviour is an intrinsic property of Ca2+i homeostasis in basket cells. 6. We conclude that depolarization of basket cell axons evokes high local Ca2+i signals in synaptic terminals, en passant varicosities and branch points. While high [Ca2+]i in presynaptic structures presumably triggers transmitter release, Ca2+i transients at branch points may control signal transmission in the axonal arborization.
Llano
I
I
Max-Planck-Institut für Biophysikalische Chemie, Göttingen, Germany. illano@gwdg.de
Tan
Y P
YP
Caputo
C
C
D000818:Animals; D001369:Axons / Q000737:chemistry / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology; D002525:Cerebellar Cortex / Q000166:cytology*; D003712:Dendrites / Q000737:chemistry / Q000502:physiology; D007091:Image Processing, Computer-Assisted; D008239:Lysine / Q000031:analogs & derivatives; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D011154:Population Characteristics; D051381:Rats
D015220:Calcium Channels; C013411:biocytin; D008239:Lysine; D002118:Calcium