Figure 2.

Time course of ⁸⁶Rb⁺ (*K⁺) influx into rabbit red cells at 37°C from a medium consisting of (mM): 155 NaCl, 5 KCl, 10 HEPES, 10⁻⁴ M ouabain. In two of the suspensions (•, ▪), the pH was initially 7.5 and was lowered to 6.8 at t = 12.5 min by addition of 18 mM MOPS and 5 mM NaHCO₃. The solid curve through the data corresponds to a single exponential increase in flux, with a lag time of 14 min. In the other two suspensions (▴, ▾), the pH was lowered to 6.8 by adding 18 mM MOPS and 5 mM NaHCO₃ 15 min before adding ⁸⁶Rb⁺; the pH of these suspensions was raised to 7.9 at t = 12.5 min by addition of NaOH. The curve through these data is , with a lag time of 3.6 min.