Figure 5. PIP₂-Dependent Modulation of Ca_V2.2 N-type channels.

(A) Ca_V2.2 current density (pA/pF) was measured in cells expressing the Ca_V2.2 channels plus GFP, GFP-PH-PLCδ1, or YFP-PH-Akt. The cells were transfected with the same amounts of cDNA. Average membrane capacitances for cells are 22 ± 2 pF for GFP (n = 11), 25 ± 4 for PH-PLC (n = 11), and 24 ± 4 for PH-Akt (n = 12). Top, Confocal images of tsA cells expressing each fluorescent protein. Cell diameters were 20 - 30 μm.

(B) Elevated PIP₂ levels attenuate Ca_V2.2 channel inhibition by M₁ receptor stimulation. Ca_V2.2 currents were measured in control cells and in cells transfected with PIPKIγ. Right, Summary of current inhibition by Oxo-M. Data are mean ± SEM. *P < 0.05, compared to control.

(C) Current-voltage (I-V) relations of N-type Ca_V current in isolated rat SCG neurons expressing Dr-VSP (n = 3) with a widefield image of one neuron.

(D) Inhibition of N-type Ca_V currents by Dr-VSP activation in SCG neurons. N-type Ca_V currents were measured during test pulses before and after a +120-mV/1-s depolarizing pulse in control and cells expressing Dr-VSP. Capacitive and leak currents were subtracted by a P/5 procedure. Right, Summary of N-type current inhibition by Dr-VSP activation in SCG neurons. Data are mean ± SEM (n = 3 for control, n = 3 for Dr-VSP).