INTRAVASAL USE OF PLIABLE K-SELECTIVE ELECTRODES IN THE FEMORAL VEIN OF HUMANS DURING EXERCISE()

Continuous recording of plasma K+ concentration ([K+]) during exercise would be valuable in determining K+ fluxes associated with muscle act ivation. Pliable polyvinyl chloride electrodes were constructed by inc orporation of valinomycin into a polyvinyl chloride membrane attached to the end of a catheter with a 1 mm outer diameter. Through an outer catheter the electrode was inserted into the femoral vein of human sub jects. The setup allowed easy in vivo calibration, and rapid changes o f femoral venous [K+] of <0.1 mmol/l could easily be detected. Drift o ver 1 h amounted to <3 mV and was corrected for by analysis of blood s amples. Rapid changes in femoral venous [K+] occurred during and after dynamic exercise, short and prolonged isometric contractions, and rep etitive isometric contractions of the quadriceps muscle. Combined with arterial blood sampling and flow measurements, the electrodes will al low good approximation of 1) cellular K+ efflux rate associated with i ncreased electrical activity, 2) rate of intramuscular reuptake of Kmediated by the Na+-K+ pump, and 3) rate of K+ loss to or uptake from the circulation by the muscle.