The transport of potassium in normal and dystrophic mouse muscle

Abstract

The kinetics of movement of cations between muscle cells and their environment has been the subject of much work in recent years. The largest part of this work has been on the muscles of frog, and relatively little attention has been paid to mammalian tissues other than diaphragm (Creese, 1954, 1960). The present study extends some earlier work (McLennan, 1955) with mammalian skeletal muscle, and compares also the behaviour of normal tissues and those derived from animals which had developed an inherited muscular dystrophy. METHODS The mice used were from a pure strain maintained at the University of British Columbia derived from the Bar Harbour 129 strain. This strain develops a disorder of muscle transmitted as an autosomal recessive trait which closely resembles human progressive muscular dystrophy both genetically and histologically (Michelson, Russell & Harman, 1955). Litter-mates which did not develop the condition provided normal controls. All experiments were carried out in vitro with m. gastrocnemius weighing 15-25 mg. The tissues were excised, weighed on a small torsion balance and incubated by allowing them to float freely in approx. 50 ml. of the desired saline medium in a bath set at 350 C. To measure the uptake of labelled ion the muscles were removed at intervals from the incubation medium, rinsed for exactly 1 min in a solution of identical ionic composition but without radioactive tracer, and placed beneath an end-window Geiger-Muller tube. Care was taken to ensure that the geometry of the relationship between tissue and detector was the same for each measurement. After counting for three 1 min periods the tissues were returned to the incubation medium. At the end of the experiment the tissue was dissolved in a few drops of concentrated nitric acid, diluted to 2 ml. and the radioactivity of the solution compared to that of a dilution of the incubating fluid. In this way a cross-relationship between K in the tissue and counts per minute could be established. The same solution of the muscle was used for analysis of the total tissue Na and K by the use of a flame photometer. The isotope used was 42K. Its disintegration was detected with the aid of a Geiger-Miller tube connected to a scaler unit. All radioactive counts were corrected for decay, background and resolution time of the counter-scaler combination. The solutions used for incubation were variants upon one containing (m-mole/l.): Na 144, K6, Ca 2, Mg 1, Cl 134, HCO3 20, S04 1, glucose 10, and vigorously bubbled with 95 % 02+5 % CO2. That this condition was adequate for maintenance of the normal metabolism