Figure 4. Sensitivity to hyperosmolarity partially resides in the channel domain.

A, average time-course of overexpressed murine TRPM7 currents where cells were superfused with solutions adjusted to 200 mosmol l⁻¹ but intracellular standard solution was supplemented with 3 mm free Mg²⁺ in the absence of Mg·ATP (n = 6). Error bars represent s.e.m.B, I–V relationship taken from an example cell from D before application of 200 mosmol l⁻¹ (300 s, thin trace) and at the end of application (500 s, thick trace). C, average time-course of overexpressed murine TRPM7 currents where cells were superfused with solutions adjusted to 200 mosmol l⁻¹ but intracellular standard solution was supplemented with 4 mm Mg·ATP with free Mg²⁺ adjusted to 0.9 mm (n = 5). Error bars represent s.e.m.D, I–V relationship taken from an example cell from F before application of 200 mosmol l⁻¹ (300 s, thin trace) and at the end of application (500 s, thick trace). E, average time-course of overexpressed human TRPM7 outward currents where cells were superfused with solutions adjusted to either 200 mosmol l⁻¹ or 580 mosmol l⁻¹ as indicated by the black bars. Hyperosmolarity was achieved by adding appropriate amounts of either NaCl (□, n = 6), sucrose (^, n = 5) or glucose (▪, n = 4). Hypo-osmolarity was achieved by omission of NaCl (•, n = 4). Currents were elicited by a voltage ramp from −100 mV to +100 mV over 50 ms at 0.5 Hz intervals. Current amplitudes were extracted at +80 mV, averaged and plotted versus time with error bars representing s.e.m. Cells were perfused with the standard intracellular Cs-based solution in the absence of Mg·ATP, with 0.9 mm free Mg²⁺ and 10 mm Cs-BAPTA. Error bars represent s.e.m.F, average time-course of overexpressed human Δ-kinase TRPM7 outward currents where cells were superfused with a solution adjusted to 480 mosmol l⁻¹ using sucrose (^, n = 3) or with a solution adjusted to 200 mosmol l⁻¹ by omission of NaCl (•, n = 4). Application as indicated by the black bar. Cells were perfused with the standard intracellular Cs-based solution in the absence of Mg·ATP, with 0.4 mm free Mg²⁺ and 10 mm Cs-BAPTA. Error bars represent s.e.m.G, I–V relationship taken from an example cell before application of 200 mosmol l⁻¹ (300 s, thin trace) and at the end of application (500 s, thick trace). The inset magnifies the inward currents. H, average time-course of overexpressed human Δ-kinase TRPM7 outward currents in the absence of intracellular magnesium, where cells were superfused with a solution adjusted to 200 mosmol l⁻¹ (•, n = 5). Data were normalized to the current measured before application as I/I_200s. Application as indicated by the black bar.