Measurements of the intracellular diffusion coefficients (Di) of ATP and creatine phosphate (PCr) in stable, isolated preparations of skeletal muscle were made by means of pulsed field gradient (PFG) 31P NMR. Experiments used a PFG NMR probe specifically designed for small, superfused biological samples. This provided a magnetic field gradient in the z axis of up to 195 G/cm with minimal eddy currents. DiATP and DiPCr in white (fast, glycolytic) skeletal muscle from goldfish (Carassius auratus) were determined to be 2.48 +/- 0.33 and 3.49 +/- 0.33 x 10(-6) cm2/s, respectively, at 25 degrees C and a diffusion time of approximately 19 ms. For comparison with Di values, diffusion coefficients of ATP and PCr also were measured in solutions of ionic composition similar to that of fish muscle cytosol. The in vitro diffusion coefficients of ATP and PCr were 3.54 +/- 0.11 and 5.28 +/- 0.08 x 10(-6) cm2/s, respectively, at 25 degrees C.
Pulsed field gradient (PFG) spin echo 31P NMR can be used to measure diffusion coefficients of phosphorus-containing metabolites in vivo. In biological spin echo spectra, the ATP resonances are phase modulated by J-coupling between the three phosphorus atoms. This phase modulation may severely decrease the apparent signal intensity of the ATP peaks. In this paper, we describe the use of homonuclear decoupling during spin evolution to suppress the effects of J-coupling in biological spin echo spectra. Phosphorous spectra of ATP and creatine phosphate (PCr) in solution and goldfish (Carassius auratus) skeletal muscle demonstrate the effectiveness of homonuclear decoupling in improving the effective signal-to-noise ratio of ATP. In addition, diffusion coefficients of ATP and PCr determined in goldfish skeletal muscle show that PFG homonuclear decoupled spin echo (HDSE) NMR provides accurate measures of diffusion coefficients.
Abstract. Populations of Marenzelleria viridis in the Chester River (Kent County, Maryland) experience temperatures ranging from over 30°C in summer to near freezing in winter. Interestingly, M. viridis swims actively in winter. This observation led us to examine the relationship between locomotor capacity and temperature in individuals of M. viridis. Juvenile specimens were collected in February (“cold animals”) and June (“warm animals”). Video analysis revealed that swimming is achieved by flexing the body in cyclic, helical waves. Wave frequencies were measured as an index of locomotor capacity at 5°C, 15°C, and 25°C. The mean wave frequencies of cold animals were 5.4 Hz at 5°C and 7.1 Hz at 15°C (Q10= 1.3); the mean wave frequencies of warm animals were 6.1 Hz at 15°C and 7.8 Hz at 25°C (Q10= 1.3). The effects of changes in water viscosity on wave frequency between 5–25°C were not significant. These results demonstrate that the temperature sensitivity of locomotor capacity in juvenile M. viridis is quite low. We conclude that low temperature sensitivity enables M. viridis to be active throughout the year.
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