Fig. 6.

Sodium dependence of ETTh-mediated uptake of ET and stachydrine. Cells were rapidly washed with modified uptake buffers in which N-methyl-d-glucosamine isoosmotically substituted Na⁺ as indicated and then assayed for uptake in the same buffer. Control uptake buffers were completely free of Na⁺. Shown is mean ± SEM (n = 3) of specific initial rates of uptake (uptake period, 1 min). From curve fitting of ET data, a Hill coefficient of 1.1 resulted. For stachydrine, a K_i of 114 mmol/liter was obtained.