Interstitial K1 in human skeletal muscle during and after dynamic graded exercise determined by microdialysis

Juel, C., H. Pilegaard, J. J. Nielsen, and J. Bangsbo. Interstitial K1 in human skeletal muscle during and after dynamic graded exercise determined by microdialysis. Am. J. Physiol. Regulatory Integrative Comp. Physiol. 278: R400– R406, 2000.—Interstitial K1 concentrations were measured during one-legged knee-extensor exercise by use of microdialysis with probes inserted in the vastus lateralis muscle of the subjects. K1 in the dialysate was measured either by flame photometry or a K1-sensitive electrode placed in the perfusion outlet. The correction for fractional K1 recovery was based on the assumption of identical fractional thallium loss. The interstitial K1 was 4.19 6 0.09 mM at rest and increased to 6.17 6 0.19, 7.48 6 1.18, and 9.04 6 0.74 mM at 10, 30, and 50 W exercise, respectively. The individual probes demonstrated large variations in interstitial K1, and values .10 mM were obtained. The observed interstitial K1 was markedly higher than previously found for venous K1 concentrations at similar work intensities. The present data support a potential role for interstitial K1 in regulation of blood flow and development of fatigue.