Figure 1. The stimulus-response relationship between medium osmolarity and NHE1 Na⁺ transport activity in atRBCs.

Unidirectional Na⁺ influx rates (²²Na⁺ initial rates) were measured in hyperosmotic media at a fixed media [Na⁺] = 100 mM, following complete activation of NHE1 by pre-incubation in thermodynamically nulled media of matched osmolarity. The data are fit to a sigmoidal curve by non-linear regression (Hill slope = 4.1), yielding a maximal Na⁺ influx rate of 13.2 mmoles Na⁺ kg⁻¹ dcs minute. (data are n≥5 each; ± SE).