Pulsed nuclear magnetic resonance study of 39K in frog striated muscle

• Published in: Biophysical journal Vol. 16; no. 12; pp. 1385 - 1398
• Main Authors: Civan, M.M., McDonald, G.G., Pring, M., Shporer, M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.12.1976
• Subjects: Animals; Female; In Vitro Techniques; Magnetic Resonance Spectroscopy; Male; Muscles - analysis; Potassium - analysis; Rana pipiens
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(76)85782-7

Samples of 1 M KCl solution and 10 samples of intact frog striated muscle were studied at 4–7 degrees C and/or at 21–22 degrees C. Field inhomogeneity was minimized by using small sample volumes and by using a superconducting magnet designed specifically to provide highly homogeneous fields. In the present experiments, magnetic field inhomogeneity was measured to contribute less than 15% to the free induction decay observed for intracellular 39K. The signal-to-noise ratio of the measurements was enhanced by means of extensive time-averaging. The rates of nuclear relaxation for 39K in aqueous solution were 22 +/- 3 (mean +/- 95% confidence limits) s-1 at 4–7 degrees C and 15 +/- 2 s-1 at 21–22 degrees C. For intracellular 39K, (1/T2) was measured to be 327 +/- 22 s-1 and 229 +/- 10 s-1 at the lower and higher temperatures, respectively. The corresponding values for (1/T1) in the same muscle samples were 198 +/- 31 s-1 and 79 +/- 15 s-1 at 4–7 degrees C and at 21–22 degrees C, respectively. These results for 39K are similar to those previously obtained for intracellular 23Na. Since less than 1% of the intracellular 23Na has been estimated to be immobilized, fractional immobilization of intracellular 39K is also likely to be insubstantial.