POTASSIUM EXCHANGE IN PERFUSED MAMMALIAN 

 SKELETAL MUSCLE* 



E. M. RENKIN 



A variety of isolated mammalian cells and tissues immersed in saline fluids have 

 been found to suffer a net loss of potassium ion in the cold. These include red blood 

 cells/' - white blood cells^ and skeletal muscles.^ Measurements of K"^ exchange 

 rates with radioactive K*- indicate that (1) both influx and outflux of K^ are re- 

 duced at low temperatures and (2) influx is reduced to the greater extent, and net 

 loss results. In the case of frog muscles, influx and outflux are equally reduced in 

 the cold, and tissue K"^ balance is maintained at temperatures as low as 0° C.° 



Dr. Taylor has found that in the rat's heart perfused with a saline medium, K"^ 

 balance is maintained at 8° C.'' My own observations on perfused mammalian skele- 

 tal muscle demonstrate that this tissue, when perfused rather than immersed, is also 

 capable of maintaining its intracellular IC level in the cold, at temperatures down to 

 3° C. Tracer equilibration experiments with K^- show that Ik influx is reduced at 

 low temperatures, and since IC balance was maintained, K"^ outflux must be reduced 

 to the same extent. 



The experimental procedure was as follows. The hind leg of a cat was amputated 

 at the hip joint and arranged to be perfused through the femoral artery by a me- 

 chanical pump-oxygenator. The perfusion fluid was either fresh cat blood diluted 

 with Ringer's solution or a solution of purified hemoglobin in cat plasma. Heparin 

 was used as anticoagulant. The outflow of perfusate from the femoral vein was 

 returned to the perfusion reservoir, thus a fixed volume of fluid, 150 to 200 ml., 

 was recirculated through the tissues. Blood flows were maintained at normal resting 

 levels or higher, 3 to 10 ml./min. per 100 gm. The weight of the perfused prepara- 

 tion was usually between 300 and 400 gm. ; 80 per cent of this was skeletal muscle. 



The total amount of K^ in the perfusion fluid was small compared to the amount 

 in the tissues of the hind leg: 4.3 mEq./L. x0.2L. = 0.86 mEq. compared to 

 75. mEq./kgm. xO.3 kgm. = 22.5 mEq. Consequently, if a small amount of K* was 

 lost by the tissues, it produced a large rise in plasma [K*|. Figure 1 illustrates the 

 time-course of plasma [K"^] in typical perfusions at 35° C. and at 3° C. At 35°, after 

 remaining constant for an hour, plasma [K"^] rose linearly, indicating net loss from 

 the tissues at 1.5 niEq./hr. or 0.02 per cent tissue K* per minute. The reason for net 

 loss at body temperature is not known. It is relatively slight, and does not appear 

 to be related to injury to the tissues during preparation of the hindleg, glucose con- 

 tent of the perfusion fluid, or the presence or absence of red blood cells in the per- 

 fusion fluid. The delayed onset of the loss suggests that accumulation of non-vola- 

 tile metabolites in the perfusion medium may be responsible, since no provision 

 exists for their removal in tlie perfusion circuit. It is interesting to note, in this con- 

 nection, that Andres and others' reported net loss of K' from the forearm muscles 



*The experiments reported here were carried out in the Biology Department, Brookhaven 

 National Laboratory, Upton, New York, under the auspices of the U.S. Atomic Energy 

 Commission. 



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