TY - JOUR
T1 - Differential occurrence of reluctant openings in G-protein-inhibited N- and P/Q-type calcium channels
AU - Colecraft, Henry M.
AU - Patil, Parag G.
AU - Yue, David T.
PY - 2000
Y1 - 2000
N2 - Voltage-dependent inhibition of N- and P/Q-type calcium channels by G proteins is crucial for presynaptic inhibition of neurotransmitter release, and may contribute importantly to short-term synaptic plasticity. Such calcium-channel modulation could thereby impact significantly the neuro-computational repertoire of neural networks. The differential modulation of N and P/Q channels could even further enrich their impact upon synaptic tuning. Here, we performed in-depth comparison of the G-protein inhibition of recombinant N and P/Q channels, expressed in HEK 293 cells with the m2 muscarinic receptor. While both channel types display classic features of G-protein modulation (kinetic slowing of activation, prepulse facilitation, and voltage dependence of inhibition), we confirmed previously reported quantitative differences, with N channels displaying stronger inhibition and greater relief of inhibition by prepulses. A more fundamental, qualitative difference in the modulation of these two channels was revealed by a modified tail-activation paradigm, as well as by a novel 'slope' analysis method comparing time courses of slow activation and prepulse facilitation. The stark contrast in modulatory behavior can be understood within the context of the 'willing-reluctant' model, in which binding of G-protein βγ subunits to channels induces a reluctant mode of gating, where stronger depolarization is required for opening. Our experiments suggest that only N channels could be opened in the reluctant mode, at voltages normally spanned by neuronal action potentials. By contrast, P/Q channels appear to remain closed, especially over these physiological voltages. Further, the differential occurrence of reluctant openings is not explained by differences in the rate of G-protein unbinding from the two channels. These two scenarios predict very different effects of G-protein inhibition on the waveform of Ca2+ entry during action potentials, with potentially important consequences for the timing and efficacy of synaptic transmission.
AB - Voltage-dependent inhibition of N- and P/Q-type calcium channels by G proteins is crucial for presynaptic inhibition of neurotransmitter release, and may contribute importantly to short-term synaptic plasticity. Such calcium-channel modulation could thereby impact significantly the neuro-computational repertoire of neural networks. The differential modulation of N and P/Q channels could even further enrich their impact upon synaptic tuning. Here, we performed in-depth comparison of the G-protein inhibition of recombinant N and P/Q channels, expressed in HEK 293 cells with the m2 muscarinic receptor. While both channel types display classic features of G-protein modulation (kinetic slowing of activation, prepulse facilitation, and voltage dependence of inhibition), we confirmed previously reported quantitative differences, with N channels displaying stronger inhibition and greater relief of inhibition by prepulses. A more fundamental, qualitative difference in the modulation of these two channels was revealed by a modified tail-activation paradigm, as well as by a novel 'slope' analysis method comparing time courses of slow activation and prepulse facilitation. The stark contrast in modulatory behavior can be understood within the context of the 'willing-reluctant' model, in which binding of G-protein βγ subunits to channels induces a reluctant mode of gating, where stronger depolarization is required for opening. Our experiments suggest that only N channels could be opened in the reluctant mode, at voltages normally spanned by neuronal action potentials. By contrast, P/Q channels appear to remain closed, especially over these physiological voltages. Further, the differential occurrence of reluctant openings is not explained by differences in the rate of G-protein unbinding from the two channels. These two scenarios predict very different effects of G-protein inhibition on the waveform of Ca2+ entry during action potentials, with potentially important consequences for the timing and efficacy of synaptic transmission.
KW - Channel modulation
KW - Heterologous expression
KW - Short-term synaptic plasticity
KW - α(1A)
KW - α(1B)
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U2 - 10.1085/jgp.115.2.175
DO - 10.1085/jgp.115.2.175
M3 - Article
C2 - 10653895
AN - SCOPUS:0033818977
SN - 0022-1295
VL - 115
SP - 175
EP - 192
JO - Journal of General Physiology
JF - Journal of General Physiology
IS - 2
ER -