Muscle ammonia stores are not determined by pH gradients

The theory of non-ionic diffusion predicts that ammonia will distribute between intracellular and extracellular tissue compartments according to transmembrane pH gradients. The distribution of ammonia and¹⁴C-DMO were compared in white muscle and plasma of rainbow trout (Salmo gairdneri) at rest, and following exhaustive exercise. Under both experimental conditions, intracellular ammonia levels far exceeded those predicted by transmembrane pH gradients. Calculated equilibrium potentials for\(NH_4^ + (E_{NH_4^ + } )\)) were very close to published resting values of membrane potential E_m in fish white muscle. We conclude that NH ⁺₄ is permeable across cell membranes and that intracellular ammonia stores are not determined by pH gradients.