Gating charges per channel of Cav2.2 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 GTP gamma S reduced elementary charge by similar to 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. (C) 2009 Elsevier Inc. All rights reserved.