Gating charges per channel of Ca(V)2.2 channels are modified by G protein activation in rat sympathetic neurons.
It has been suggested that voltage-dependent G protein modulation of Ca(V)2.2 channels is carried out at closed states of the channel. Our purpose was to estimate the number of gating charges of Ca(V)2.2 channel in control and G protein-modulated conditions. By using a Cole-Moore protocol we observed a significant delay in Ca(V)2.2 channel activation according to a transit of the channel through a series of closed states before channel opening. If G protein voltage-dependent modulation were carried out at these closed states, then we would have expected a greater Cole-Moore lag in the presence of a neurotransmitter. This prediction was confirmed for noradrenaline, while no change was observed in the presence of angiotensin II, a voltage-insensitive G protein modulator. We used the limiting slope method for calculation of the gating charge per channel. Effective charge z was 6.32+/-0.65 for Ca(V)2.2 channels in unregulated conditions, while GTPgammaS reduced elementary charge by approximately 4 e(0). Accordingly, increased concentration of noradrenaline induced a gradual decrease on z, indicating that this decrement was due to a G protein voltage-sensitive modulation. This paper shows for the first time a significant and reversible decrease in charge transfer of Ca(V)2.2 channels under G protein modulation, which might depend on the activated G protein inhibitory pathway.
Rebolledo-Antúnez
Santiago
S
Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México (UNAM), Av. Universidad 3000, Ciudad Universitaria, Delegación Coyoacán, C.P. 04510, Apdo. Postal 70250, México, D.F., Mexico.
Farías
José M
JM
Arenas
Isabel
I
García
David E
DE
D000818:Animals; D055592:Biophysical Phenomena; D020864:Calcium Channels, N-Type / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008959:Models, Neurological; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D017783:Superior Cervical Ganglion / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013873:Thionucleotides / Q000378:metabolism / Q000494:pharmacology
C503279:Cacna1b protein, rat; D020864:Calcium Channels, N-Type; D013873:Thionucleotides; D006153:Guanosine Diphosphate; C023427:guanosine 5'-O-(2-thiodiphosphate); D019204:GTP-Binding Proteins; D009638:Norepinephrine