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Facilitation of rabbit α 1B calcium channels: involvement of endogenous Gβγ subunits
Author(s) -
Stephens Gary J.,
Brice Nicola L.,
Berrow Nicholas S.,
Dolphin Annette C.
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.015bo.x
Subject(s) - chemistry , prepulse inhibition , depolarization , biophysics , facilitation , inhibitory postsynaptic potential , endogeny , protein subunit , neuroscience , biochemistry , biology , psychology , schizophrenia (object oriented programming) , psychiatry , gene
1 The α 1B (N‐type) calcium channel shows strong G protein modulation in the presence of G protein activators or Gβγ subunits. Using transient expression in COS‐7 cells of α 1B together with the accessory subunits α 2 ‐δ and β 2a , we have examined the role of endogenous Gβγ subunits in the tonic modulation of α 1B , and compared this with modulation by exogenously expressed Gβγ subunits. 2 Prepulse facilitation of control α 1B /α 2 ‐δ/β 2a currents was always observed. This suggests the existence of tonic modulation of α 1B subunits. To determine whether endogenous Gβγ is involved in the facilitation observed in control conditions, the βARK1 Gβγ‐binding domain (amino acids 495‐689) was overexpressed, in order to bind free Gβγ subunits. The extent of control prepulse‐induced facilitation was significantly reduced, both in terms of current amplitude and the rate of current activation. In agreement with this, GDPβS also reduced the control facilitation. 3 Co‐expression of the Gβ 1 γ 2 subunit, together with the α 1B /α 2 ‐δ/β 2a calcium channel combination, resulted in a marked degree of depolarizing prepulse‐reversible inhibition of the whole‐cell I Ca or I Ba . Both slowing of current activation and inhibition of the maximum current amplitude were observed, accompanied by a depolarizing shift in the mid‐point of the voltage dependence of activation. Activation of endogenous Gβγ subunits by dialysis with GTPγS produced a smaller degree of prepulse‐reversible inhibition. 4 The rate of reinhibition of α 1B currents by activated G protein, following a depolarizing prepulse, was much faster with Gβ 1 γ 2 than for the decay of facilitation in control cells. Furthermore, βARK1 (495‐689) co‐expression markedly slowed the control rate of reinhibition, suggesting that the kinetics of reinhibition depend on the concentration of free endogenous or exogenously expressed Gβγ in the cells. In contrast, the rate of loss of inhibition during a depolarizing prepulse did not vary significantly between the different conditions examined. 5 These findings indicate that, in this system, the voltage‐dependent facilitation of α 1B that is observed under control conditions occurs as a result of endogenous free Gβγ binding to α 1B .