EFFECT OF CURARE CONCENTRATION, TEMPERATURE AND POTASSIUM ION CONCENTRATION ON THE RATE OF UPTAKE OF A NEURO MUSCULAR BLOCKING AGENT LABELED WITH RADIOACTIVE IODINE

¹ Department of Pharmacology and Brain Research Institute, University of California Medical Center, Los Angeles, California, and Department of Physiology, St. Mary's Hospital Medical School, London, W. 2, England

The uptake of iodocholinium by voluntary muscle can be divided into three components. First, there is the component which diffuses into the tissue spaces between the muscle fibers; secondly, the tissue elements take up some iodocholinium and this is unaffected by curare; and finally, there is a considerable uptake which is very sensitive to and decreased by increasing curare concentration.

The curare-sensitive component of iodocholinium uptake is exponentially related to curare concentration. An approximate value has been suggested for the value of the curare receptor dissociation constant.

The influence of temperature changes on the curare-sensitive and curare-insensitive components of iodocholiniurn uptake has been determined. The data for uptake as a function of temperature can be fitted to the Arrhenius equation and values of approximately 21,000 cals mol^-1 for the activation energy of the curare sensitive component and of 7,300 cals for the curare insensitive component have been estimated. The higher value for the curare-sensitive component is consistent with membrane penetration, while that for the curare-insensitive component does not necessarily indicate such a process.

Increase in potassium ion concentration decreases the ability of curare to prevent iodocholinium uptake.