Figure 4.

Electrophysiological Characterization of DmHKT1 Expressed in Xenopus Oocytes and Sodium Flux Measurements in Dionaea Glands

(A) Representative sodium-induced inward currents at a membrane potential of −140 mV could be recorded in DmHKT1-expressing oocytes (red line), while water-injected cells (control) did not show sodium-dependent current responses (black line).

(B) Steady-state currents (I_SS) recorded from DmHKT1-expressing oocytes at −140 mV were plotted as a function of the sodium concentration, and the saturation curve was fitted with a Michaelis-Menten equation. This gave a K_m value of 10 mM ± 1.04 for sodium ions (n = 3, mean ± SD).

(C) MIFE experiments with COR-treated Dionaea traps were performed to simultaneously record net Na⁺ and K⁺ influxes in response to varying external Na⁺ concentrations, as indicated in the figure. Increasing external sodium concentrations elevated Na⁺ influxes up to peak values of ∼1,800 nmol m⁻² s⁻¹. In contrast, K⁺ fluxes were unaffected by changes in the external Na⁺ concentration, remaining close to 0. A representative MIFE measurement from 12 independent measurements is shown.

(D) Representative membrane potential measurement from a DmHKT1-expressing oocyte revealed Na⁺-specific membrane potential depolarizations. The perfusion protocol is given within the figure, and the osmolarity was maintained at 240 mOsm/kg with NMDG-Cl.

See also Figure S3.