Fractional Ca2+ current through human neuronal α7 nicotinic acetylcholine receptors

The neuronal α7 nicotinic acetylcholine (ACh) receptor is believed to be a highly Ca²⁺ permeable ligand-gated receptor-channel. However, the contribution of Ca²⁺ to cationic current generated by ACh has not yet been directly measured to date. Simultaneous fluorescence and whole-cell current measurements using the Ca²⁺ indicator dye fura-2 were made in GH4C1 pituitary cells stably expressing human α7 receptors and the fractional Ca²⁺ current (the proportion of whole-cell current carried by Ca²⁺; P_f) was determined. We report that the P_f value was 11.4 ± 1.3%. This value was significantly larger than P_f of human L248Tα7 receptor mutant (P_f = 6.3 ± 1.0%) and of rat α7 receptor (P_f = 8.8 ± 1.5 %) both determined in transiently transfected GH4C1 cells. In our knowledge, the findings here reported indicate the human α7 receptors are the most Ca²⁺ conductive homomeric ligand-gated receptor-channels expressed in a heterologous cell system.