The effects of temperature, pH, and magnesium on the diffusion coefficient of ATP in solutions of physiological ionic strength

Abstract

Intracellular diffusive transport of adenosine triphosphate (ATP) is critical to cellular metabolism. Physical models predict that diffusion coefficients ( D) of small molecules are functions of temperature and viscosity of the diffusive environment. Therefore, changes in body temperature, commonly experienced by poikilotherms, are expected to result in changes in the rate of intracellular ATP transport. However, it has been postulated that changes in the electrical charge of ATP may influence the interaction between ATP and the cytosol and that the temperature sensitivity of D ATP may deviate from the predicted relationship. To investigate the effects of changes in electrical charge on the temperature sensitivity of D ATP, we measured D ATP under various conditions of temperature, pH, and pMg 2+. Changes in pH and pMg 2+ were used to alter the net charge of ATP, and D ATP was measured in solutions of physiological ionic strength. Results showed a positive correlation between D ATP and temperature; D ATP = 1.75 ± 0.09, 3.68 ± 0.14, and 4.64 ± 0.13 (mean ± S.E.M.) × 10 −6 cm 2/s at 5°C, 25°C, and 40°C, respectively. Changes in pH and pMg 2+ did not significantly influence D ATP, and the change in D ATP with respect to temperature was similar to that predicted on the basis of changes in temperature and viscosity of the aqueous medium.