Figure 3. Ca²⁺ permeability of human γ-AChR.

A, left-hand traces show simultaneous recordings of whole-cell current (top) and Ca²⁺ transient (bottom), induced by nicotine (100 μm, horizontal thin line), in a GH4C1 cell transiently transfected with wild-type αβγδ AChR subunit cDNAs. Holding potential, −70 mV. At the excitation wavelength of 380 nm, [Ca²⁺]_i increase corresponds to a downward deflection of fluorescence intensity. Traces are aligned and share the same temporal scale. Middle panel shows typical epifluorescence image of a GH4C1 cell dialysed with Fura-2 through the patch pipette (halo on the right). Contrast was adjusted to increase the visibility of nucleus. Graph on the right shows linear relationships between ΔF/F and Q obtained from the same cell. For this example, the P_f value, calculated by normalizing the slope obtained in A (standard medium) to the mean slope obtained from calibration experiments (dashed line), is 3.2%. B, left-hand traces show simultaneous recordings of whole-cell current (top) and Ca²⁺ transient (bottom), induced by nicotine (100 μm, horizontal thin line), from a human myotube. Holding potential, −70 mV. Traces are aligned and share the same temporal scale. Middle panel shows typical fluorescence image of a binucleated human myotube dialysed with Fura-2. Graph on the right shows linear relationship between ΔF/F and Q obtained from the cell shown in B. For this example, the P_f value, calculated by normalizing the slopes obtained in B (standard medium) with respect to the mean slope obtained from calibration experiments (3.07 nC⁻¹; dashed line), is 2.9%.