Correlation between Na, K-ATPase activity and potassium and magnesium contents in skeletal muscle of renal stone patients.

Samples of external oblique muscles were surgically removed from 45 renal stone patients and analyzed for their K, Na and Mg content. The muscle samples were also measured for membrane Na, K-ATPase activity from the assay of its K+-dependent 3-0-methyl fluorescein phosphatase (K+-dependent 3-0-MFPase) activity. The results showed that the mean muscle contents +/- SEM of K, Na and Mg were 65.2 +/- 1.7 (range, 41.1 to 86.1), 45.5 +/- 2.0 (range, 23.5 to 73.2) and 6.3 +/- 1.0 (range, 4.1 to 8.5) micromol/g wet weight, respectively. The mean activity +/- SEM of the K+-dependent 3-0-MFPase or the Na, K-ATPase was calculated by subtracting the activity of the basal-form from that of the total-3-0-MFPase, which was 113 +/- 21 (range, 11 to 177) nmol/g wet weight/minute. The activity of the Na, K-ATPase showed a significant correlation with muscle K-content (r = 0.52, p<0.001) and Mg content (r = 0.45, p<0.002). Though the external oblique muscles of renal stone patients in our study, as compared to data from other sources, had a considerably low concentration of K and Mg, they exhibited a good correlation with membrane-Na, K-ATPase activity. Our results, therefore, support previous observations made by other investigators.

Potassium, sodium and magnesium contents in skeletal muscle of renal stone-formers: a study in an area of low potassium intake.

Skeletal muscles surgically obtained from the stone-former group (external oblique muscle; n = 202, 82 males & 120 females), control group I (external oblique muscle; n = 5, all males), control group II (rectus abdominis muscle; n = 23, all females) and control group III (quadriceps femoris muscle; n = 11, all males) were analyzed for potassium (K), sodium (Na) and magnesium (Mg) contents. Muscle samples were digested with 65 per cent HNO3 and determined for K, Na and Mg by an atomic absorption spectrophotometer. The results of analysis showed the mean K, Na and Mg (+/- S.D.) contents in mumol per one gram of fresh tissue of the stone-former group, control groups I, II and III were 73.5 +/- 16.6, 51.3 +/- 13.4 and 6.6 +/- 1.3, 77.5 +/- 3.9, 43.9 +/- 9.9 and 7.2 +/- 0.5, 83.8 +/- 27.5, 49.4 +/- 24.1 and 6.7 +/- 1.8 and 85.0 +/- 17.1, 48.5 +/- 12.1 and 6.8 +/- 1.3. Among these variables, only the K content of control group III was higher significantly (p < 0.05) than that of the stone-former group. In the stone-former group, regression analysis showed significant correlations between K and Mg contents (r = 0.856, p < 0.001) and K and Na contents (r = -0.325, p < 0.001). Due to no available data of the external oblique, we made a comparison of our results to the soleus type of skeletal muscle of normal subjects reported by Dorup et al and found that the external oblique muscle had lower mean contents of K and Mg but a higher Na content than those of the soleus. Our results were similar to the K and Mg depleted muscles obtained from the patients receiving long-term treatment with diuretic drugs. The results suggest that most of our subjects in both the stone-former and the 3 control groups were in a state of K and Mg depletion. The causes may be multifactorial, for instance low intake, high sweat loss and the existence of environmental inhibitor (s) for K transport like vanadium.