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

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 DATP may deviate from the predicted relationship. To investigate the effects of changes in electrical charge on the temperature sensitivity of DATP, we measured DATP under various conditions of temperature, pH, and pMg2+. Changes in pH and pMg2+ were used to alter the net charge of ATP, and DATP was measured in solutions of physiological ionic strength. Results showed a positive correlation between DATP and temperature; DATP = 1.75 +/- 0.09, 3.68 +/- 0.14, and 4.64 +/- 0.13 (mean +/- S.E.M.) x 10(-6) cm2/s at 5 degrees C, 25 degrees C, and 40 degrees C, respectively. Changes in pH and pMg2+ did not significantly influence DATP, and the change in DATP with respect to temperature was similar to that predicted on the basis of changes in temperature and viscosity of the aqueous medium.