EARLY EFFECTS OF STREPTOMYCIN ON BACILLUS MEGATERIUM

Hancock , R. (Harvard Medical School, Boston, Mass.). Early effects of streptomycin on Bacillus megaterium . J. Bacteriol. 88: 633–639. 1964.—The sequence of some early effects of streptomycin on Bacillus megaterium was investigated. An increase in the rate of efflux of cellular K ions preceded loss of viability, but efflux of Mg ions remained normal. Loss of viability was closely coincident with reduction in rate of protein synthesis. Nucleic acid synthesis continued after protein synthesis ceased in low-phosphate medium, but ceased simultaneously with protein synthesis in normal minimal medium. Later, after viability had begun to decrease, the respiration rate began to fall and the cellular adenosine triphosphate (ATP) content decreased slowly. No leakage of ultraviolet-absorbing materials into the medium occurred, although uracil was slowly released from nucleic acid after killing had begun. It is concluded that in this organism, as previously observed with Escherichia coli , the actions of streptomycin which led to an increased rate of efflux of K and specific inhibition of protein synthesis are the only ones early enough to be of significance in its bactericidal action, the other effects being later secondary changes.

Acute subtraction alkalosis from gastric juice loss in dogs

The clinical syndrome of acute metabolic alkalosis secondary to pyloric obstruction and vomiting was simulated in 50 dogs by draining gastric juice through a cannula gastrostomy. This study was designed to quantify changes in body electrolyte and water utilizing radioisotope-dilution methods. Total body chloride decreased 43% with good correlation between the decrease in plasma chloride concentration and the decrease in total body chloride. Body sodium decreased 21% with no change in plasma sodium concentration. Body potassium decreased 20% but was not significantly related to the decrease in plasma potassium concentration. A highly significant correlation was obtained between plasma potassium and the product of blood hydrogen and intracellular potassium content. Intracellular pH (DMO) did not change significantly. Body water decreased 16% with isotonic loss of 169 mEq Na + K per liter body water. Sodium chloride solution alone corrected the alkalosis and acidified the urine. Potassium administration was necessary to prevent hypokalemia and aggravation of the cellular potassium deficit during rehydration. This study helps clarify the differences in body composition between the acute alkalosis of gastric juice loss and the alkalosis resulting from prolonged potassium depletion, sodium loading, and excess adrenocorticosteroid administration.

Potassium exchange in frog sartorius muscle

Under normal conditions, the fibers of frog sartorius muscle contain two K compartments. About two-thirds of the muscle K is in a compartment which readily exchanges with K in the extracellular fluid; the remainder of the muscle K is relatively nonexchangeable. Compartmentalization of the muscle K is not a result of high phosphate or low [K] in the Ringer's solution or previous equilibration at low temperature, but occurs also in vivo. By means of K42, the average muscle K influx and efflux in 2.5 K-Ringer's solution at 20 C were found to be (in µEq g–1 hr–1) 6.41 and 5.81, respectively (different muscles). In the steady state, K moves into the exchangeable compartment of muscle K by a process that can be described by a single exponential equation, but this mechanism fails when the energy stores of the muscle become low. K influx increases with the [K] of the Ringer's solution but reaches a maximum at high external levels of K. It is inferred from these results that the influx of K in frog muscle involves a saturable intermediate, or carrier, system.

Smooth muscle contraction in presence of an inhibitor of K efflux

Contractions of the isolated longitudinal smooth muscle from guinea pig ileum produced by pilocarpine are regularly accompanied by increases in the efflux of potassium ion. A concentration of 7.4 x 10–6 m pilocarpine produced a maximum smooth muscle contraction and an increase in potassium efflux which averaged 157% above that of unexcited fibers. In the presence of appropriate concentrations of the inhibitor (desoxycorticosterone acetate) pilocarpine evoked small to negligible increases in potassium efflux, whereas the smooth muscle contractions elicited were about 81% of the control. These data show that pilocarpine can produce a near maximal smooth muscle contraction in the absence of any pronounced change in outward flux of potassium ion.

Evaluation of Myocardial Blood Perfusion in Man with Radioactive Potassium or Rubidium and Precordial Counting

The myocardial clearance of potassium may be obtained by precordial counting after a single intravenous injection of K 42 Cl or Rb 86 Cl. The theoretical foundations of the method and the technic developed have been presented and discussed.

The distribution of the values obtained in normal subjects and in subjects with coronary insufficiency is in agreement with the clinical expectancy, and changes of the observed MCK after nitroglycerin agree with the results obtained by other investigators who measured coronary blood flow by the indirect Fick method.

In agreement with the observations of other investigators in rats and dogs, the amount of K 42 or Rb 86 in the myocardium was found to change very little for an appreciable time interval after the first circulation, despite the significant recirculation and the decreasing arterial concentration. This observation and the fact that MCK values in normal subjects closely agree with the accepted values for coronary blood flow confirm Sapirstein's findings in rats and dogs, and support the view that the organ uptake of Rb 86 or K 42 immediately after single intravenous injection reflects the fractional organ blood flow.

As obtained with the present technic, and similarly with the indirect Fick method, MCK reflects the flow per gram of myocardium and not the total coronary blood flow. MCK, however, has the advantage that every unit volume of myocardium, no matter how well it is perfused or through which vessels it is drained, contributes to the precordial counting rate in variable proportions determined by the efficiency of the counting method.

Simultaneous assay of K42, Na24, and Br82 in body composition measurements

Simultaneous measurements of Na24 and K42 specific activities may be based on chemical, physical, or metabolic differences between these two radioisotopes. This paper describes a rapid and precise technique based on both physical and metabolic differences. Two counters, a gamma-ray and a beta-ray counter, are used. Two samples are collected from each patient at tracer equilibrium (40 hr after administration of K42, 50 μc; Na24, 30 μc; Br82, 20 μc): urine, which has a high chemical K: Na ratio, and serum, which has a low chemical K: Na ratio. The urine is counted in the beta-ray counter, which favors K42. The serum is counted in the gammaray counter, which favors Na24. To calculate the specific activities, equations are used which contain appropriate decay corrections, to permit calculation of the individual specific activities even though simultaneous counting of the samples in the two detectors is not required. The laboratory procedure is simple and straightforward, and the procedure gives results which are comparable in accuracy to methods which use only one isotope at a time. When counters of great sensitivity are employed, the procedure permits both small doses of radioisotope and long equilibration periods (40 hr). Total exchangeable chloride can be estimated at the same time by Br82 dilution. The calculation has been programed for a large digital computer.

radioisotope separation; total exchangeable sodium; total exchangeable chloride; total exchangeable potassium

Submitted on September 27, 1962