Figure 6.

Na⁺and temperature dependence of DA protection of NET I155C. Cells expressing NET I155C were incubated in PBS (●) or Na⁺-free (NMDG) PBS solution (○) containing 0.25 mM MTSET for 10 min at 22°C or 1.5 mM MTSET at 4°C (■, left axis) in the presence of the indicated concentrations of DA. Cells were rinsed with PBS and assayed for DA transport in PBS at 22°C. The rate of inactivation was expressed as a pseudo first-order rate constant, assuming a simple exponential decay of the transport activity. In the absence of DA, the inactivation rate was 520 min⁻¹⋅M⁻¹ at 22°C and 61.7 min⁻¹⋅M⁻¹ at 4°C, for a Q₁₀ of 3.27. The DA concentration required for half protection increased from 0.39 μM in the presence of Na⁺ to 11.1 μM when Na⁺ was absent.