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 c ritical 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 te mperature, commonly experienced by poikilotherms, are expected to resu lt in changes in the rate of intracellular ATP transport. However, it has been postulated that changes in the electrical charge of ATP may i nfluence the interaction between ATP and the cytosol and that the temp erature sensitivity of D-ATP may deviate from the predicted relationsh ip. To investigate the effects of changes in electrical charge on the temperature sensitivity of D-ATP, we measured D-ATP under various cond itions 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 soluti ons of physiological ionic strength. Results showed a positive correla tion between D-ATP and temperature; D-ATP=1.75+/-0.09, 3.68+/-0.14. an d 4.64+/-0.13 (mean +/- S.E.M) x 10(-6) cm(2)/s at 5 degrees C, 25 deg rees C, and 40 degrees C, respectively. Changes in pH and pMg(2+) did not significantly influence D-ATP, and the change in D-ATP with respec t to temperature was similar to that predicted on the basis of changes in temperature and viscosity of the aqueous medium.