Na+-independent uptake of nutrients inTetrahymena

Summary Cell multiplication rates in cultures ofTetrahymena pyriformis andT. thermophila were independent of the external Na⁺ concentrations at the levels of 0.5, 10 and 22 mM. The Na_i/Na₀ and Cl_i/Cl₀ ratios were determined at the low and high Na⁺ concentrations, and assuming that Cl^– is distributed passively, the electrochemical Na⁺ gradients for the two situations were calculated. The energy in these gradients allows a net co-transport of nutrients only in the high Na⁺ medium. Since the doubling times are independent of the Na⁺ concentrations we conclude thatTetrahymena can obtain its energy for nutrient uptake from other sources than the electrochemical Na⁺ gradient.