Cav2.1 channels control multivesicular release by relying on their distance from exocytotic Ca2+ sensors at rat cerebellar granule cells.
The concomitant release of multiple numbers of synaptic vesicles [multivesicular release (MVR)] in response to a single presynaptic action potential enhances the flexibility of synaptic transmission. However, the molecular mechanisms underlying MVR at a single CNS synapse remain unclear. Here, we show that the Cav2.1 subtype (P/Q-type) of the voltage-gated calcium channel is specifically responsible for the induction of MVR. In the rat cerebellar cortex, paired-pulse activation of granule cell (GC) ascending fibers leads not only to a facilitation of the peak amplitude (PPFamp) but also to a prolongation of the decay time (PPPdecay) of the EPSCs recorded from molecular layer interneurons. PPFamp is elicited by a transient increase in the number of released vesicles. PPPdecay is highly dependent on MVR and is caused by dual mechanisms: (1) a delayed release and (2) an extrasynaptic spillover of the GC transmitter glutamate and subsequent pooling of the glutamate among active synapses. PPPdecay was specifically suppressed by the Cav2.1 channel blocker ω-agatoxin IVA, while PPFamp responded to Cav2.2/Cav2.3 (N-type/R-type) channel blockers. The membrane-permeable slow Ca(2+) chelator EGTA-AM profoundly reduced the decay time constant (τdecay) of the second EPSC; however, it only had a negligible impact on that of the first, thereby eliminating PPPdecay. These results suggest that the distance between presynaptic Cav2.1 channels and exocytotic Ca(2+) sensors is a key determinant of MVR. By transducing presynaptic action potential firings into unique Ca(2+) signals and vesicle release profiles, Cav2.1 channels contribute to the encoding and processing of neural information.
Department of Information Physiology, National Institute for Physiological Sciences, and School of Life Science, The Graduate University for Advanced Studies, Okazaki 444-8787, Japan.
Shin'Ichiro
S
Satake
Keiji
K
Imoto
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020864:Calcium Channels, N-Type / Q000378:metabolism*; D002531:Cerebellum / Q000378:metabolism*; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005089:Exocytosis / Q000502:physiology*; D005260:Female; D008297:Male; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D009435:Synaptic Transmission / Q000502:physiology*; D013572:Synaptic Vesicles / Q000378:metabolism*
D002118:Calcium; D020864:Calcium Channels, N-Type
Ca2+ microdomain; roscovitine; whole-cell patch clamp