title: Large Ca²⁺-dependent facilitation of Ca(V)2.1 channels revealed by Ca²⁺ photo-uncaging.
abstract: CONCLUSIONS
  CaV 2.1 channels constitute a dominant Ca(2+) entry pathway into brain neurons, triggering downstream Ca(2+) -dependent processes such as neurotransmitter release. CaV 2.1 is itself modulated by Ca(2+) , resulting in activity-dependent enhancement of channel opening termed Ca(2+) -dependent facilitation (CDF). Real-time Ca(2+) imaging and Ca(2+) uncaging here reveal that CDF turns out to be strikingly faster, more Ca(2+) sensitive, and larger than anticipated on previous grounds. Robust resolution of the quantitative profile of CDF enables deduction of a realistic biophysical model for this process. These results suggest that CaV 2.1 CDF would figure most prominently in short-term synaptic plasticity and cerebellar Purkinje cell rhythmicity.
  CaV 2.1 (P-type) voltage-gated Ca(2+) channels constitute a major source of neuronal Ca(2+) current, strongly influencing rhythmicity and triggering neurotransmitter release throughout the central nervous system. Fitting with such stature among Ca(2+) entry pathways, CaV 2.1 is itself feedback regulated by intracellular Ca(2+) , acting through calmodulin to facilitate channel opening. The precise neurophysiological role of this calcium-dependent facilitation (CDF) remains uncertain, however, in large measure because the very magnitude, Ca(2+) dependence and kinetics of CDF have resisted quantification by conventional means. Here, we utilize the photo-uncaging of Ca(2+) with CaV 2.1 channels fluxing Li(+) currents, so that voltage-dependent activation of channel gating is no longer conflated with Ca(2+) entry, and CDF is then driven solely by light-induced increases in Ca(2+) . By using this strategy, we now find that CDF can be unexpectedly large, enhancing currents by as much as twofold at physiological voltages. CDF is steeply Ca(2+) dependent, with a Hill coefficient of approximately two, a half-maximal effect reached by nearly 500 nm Ca(2+) , and Ca(2+) on/off kinetics in the order of milliseconds to tens of milliseconds. These properties were established for both native P-type currents in cerebellar Purkinje neurons, as well as their recombinant channel counterparts under heterologous expression. Such features suggest that CDF of CaV 2.1 channels may substantially enhance the regularity of rhythmic firing in cerebellar Purkinje neurons, where regularity is believed crucial for motor coordination. In addition, this degree of extensive CDF would be poised to exert large order-of-magnitude effects on short-term synaptic plasticity via rapid modulation of presynaptic Ca(2+) entry.
authors: Calcium Signals Laboratory, The Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA.|Departments of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA.
authors: Shin-Rong
authors: SR
authors: Lee
authors: Department of Biology, Kwantlen Polytechnic University, Surrey, BC, Canada, V3W 2M8.
authors: Paul J
authors: PJ
authors: Adams
authors: Calcium Signals Laboratory, The Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA.|Departments of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA.|Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA.|Center for Cell Dynamics, The Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA.
authors: David T
authors: DT
authors: Yue
mesh_terms: D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020864:Calcium Channels, N-Type / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D011689:Purkinje Cells / Q000378:metabolism / Q000502:physiology*
chemical_list: D002118:Calcium; D020864:Calcium Channels, N-Type