Figure 3. Osmosensitivity is independent of the direction of the osmotic gradient.

A, averaged outward current development of overexpressed murine TRPM7 in HEK293 cells. Cells were perfused with standard intracellular solution adjusted to 480 mosmol l⁻¹ and allowed to develop in normal (310 mosmol l⁻¹) extracellular solution. Superfusion of isotonic (480 mosmol l⁻¹) extracellular solution is indicated by the black bar (n = 4). Currents were elicited by a voltage ramp from −100 mV to +100 mV over 50 ms at 0.5 Hz intervals. Currents were extracted at +80 mV and plotted versus time. 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. Intracellular osmolarity was adjusted adding CsCl. Error bars indicate s.e.m.B, averaged outward current development of TRPM7 in HEK293. Cells were perfused with standard intracellular solution adjusted to 230 mosmol l⁻¹ and allowed to develop in normal (310 mosmol l⁻¹) extracellular solution. Superfusion of isotonic (230 mosmol l⁻¹) extracellular solution is indicated by the black bar (n = 7). Intracellular osmolarity was adjusted omitting caesium glutamate. Error bars indicate s.e.m.C, I–V relationship of an example cell perfused with 480 mosmol l⁻¹ and before (300 s, thin line) and at the end of application of 480 mosmol l⁻¹ extracellular solution (500 s, thick line). D, I–V relationship of an example cell perfused with 230 mosmol l⁻¹ and before (300 s, thin line) and at the end of application of 230 mosmol l⁻¹ extracellular solution (500 s, thick line).