Figure 5.

Potential dependence of SAAT1-mediated currents induced by different concentrations of β-d-Glc-IPM in the presence of Na⁺ (a and c) or by different Na⁺ concentrations in the presence of β-d-Glc-IPM (b and d). Ten nanograms of SAAT1-cRNA was injected into Xenopus oocytes, and the oocytes were incubated for 5 days. (a) The currents are shown that were measured when oocytes clamped at different membrane potentials were superfused with different concentrations of β-d-Glc-IPM in the presence of 100 mM Na⁺. The measurements from three oocytes were normalized to their maximal currents at −150 mV. The Michaelis–Menten equation was fitted to the data obtained at the respective membrane potential, and the K_m values were plotted against the different membrane potentials (c). The currents measured after superfusion of the oocytes with 1 mM β-d-Glc-IPM in the presence of different concentrations of Na⁺ are shown in b. Here measurements from three oocytes were normalized to their current in the presence of 100 mM Na⁺ at −100 mV. Means and SEM values are presented, and the Michaelis–Menten equation was fitted to the currents obtained at each membrane potential. The K_0.5 values for Na⁺ activation at different membrane potentials are presented in d.