The effects of temperature on diffusive transport of phosphorus metabolites in goldfish (Carassius auratus) skeletal muscle

Intracellular diffusion of the energetically important phosphorous metabolites ATP and creatine phosphate (PCr) is crucial to the function of skeletal muscle. However, the effects of temperature on intracellular diffusion of these molecules have not been examined. In this study, diffusion coefficients (D) of ATP and PCr were determined in solutions of physiological ionic composition at 5{dollar}spcirc{dollar}C, 25{dollar}spcirc{dollar}C, and 40{dollar}spcirc{dollar}C; and D{dollar}rmsb{lcub}ATP{rcub}{dollar} and D{dollar}sb{lcub}rm PCr{rcub}{dollar} were determined in goldfish skeletal muscle at 5{dollar}spcirc{dollar}C and 25{dollar}spcirc{dollar}C. In vitro studies were performed using pulsed field gradient {dollar}sp{lcub}31{rcub}{dollar}P nuclear magnetic resonance spectroscopy (PFG {dollar}sp{lcub}31{rcub}{dollar}P NMR) and Plexiglas{dollar}spcircler{dollar} diffusion cells. In vivo studies were performed using PFG {dollar}sp{lcub}31{rcub}{dollar}P NMR. Results showed that changes in temperature had a significant effect on D{dollar}rmsb{lcub}ATP{rcub} and Dsb{lcub}PCr{rcub}{dollar} in solution and in goldfish skeletal muscle. The observed Q{dollar}sb{lcub}10{rcub}{dollar}'s for both D{dollar}rmsb{lcub}ATP{rcub} and Dsb{lcub}PCr{rcub}{dollar} were 1.28 in vivo and 1.36 in vitro. This study showed that there were no significant effects of changes in pH or the concentration of Mg{dollar}sp{lcub}++{rcub}{dollar} on D{dollar}rmsb{lcub}ATP{rcub}{dollar} in solution. Furthermore, there were no significant differences in D{dollar}rmsb{lcub}ATP{rcub} or Dsb{lcub}PCr{rcub}{dollar} measured in red (oxidative) vs. white (glycolytic) muscle, or in muscle from goldfish acclimated to 25{dollar}spcirc{dollar}C vs. goldfish acclimated to 5{dollar}spcirc{dollar}C.; Measures of D{dollar}rmsb{lcub}ATP{rcub} and Dsb{lcub}PCr{rcub}{dollar} in goldfish skeletal muscle were used to analyze the effects of temperature on the spatial distributions of ATP and PCr throughout activated goldfish muscle fibers. For these calculations, a mathematical reaction-diffusion model was developed incorporating the effects of temperature on diffusion coefficients, chemical reaction rates, and intracellular diffusion distances. Results indicated that diffusion of ATP and PCr was not limiting in red muscle at 5{dollar}spcirc{dollar}C or 25{dollar}spcirc{dollar}C, regardless of acclimation temperature. This appeared due primarily to the short spacing between mitochondria in red fibers. Availability of ATP may become considerably reduced at both 5{dollar}spcirc{dollar}C and 25{dollar}spcirc{dollar}C in white muscle, which has limited capacity for sustained ATP production.