Effect of rapid and transitory changes in blood and urine pH on NH4 excretion

The Chinard technique of close arterial injection has been adapted to permit a closer study of the relationship of pH to ammonium excretion. NaHCO3, Na4Fe(CN)6, HCl, and creatinine hydrochloride solutions were injected into a renal artery of a dog undergoing osmotic diuresis while 15-sec serial urine and renal venous blood samples were being collected. Because of the difference in transit time between blood and urine the effect of the alteration in blood pH upon ammonium excretion could be seen before the filtered portion of the injection reached the urine. Thus NaHCO3 in the blood raised urine ammonium concentration while urine pH remained relatively constant. Later as NaHCO3 appeared in the urine, pH rose and urine ammonium concentration fell. Na4Fe(CN)6, which decreased blood pH, produced opposite effects. HCl and creatinine hydrochloride caused an immediate fall in both urine pH and ammonium concentration which persisted during the appearance of the injection in the urine. The results of these experiments are interpreted in terms of the theory of nonionic diffusion.

TRICOMPLEX FIXATION OF PHOSPHOLIPIDS

A basis for the interpretation of the structure of the cell membrane is often looked for in electron microscope investigations on the structure of lipid models. A difficulty in these investigations is our lack of knowledge of the effect of the preparative treatment on the structure studied. This applies especially to the strongly oxidizing fixatives: osmium tetroxide and potassium permanganate. These agents have, moreover, the drawback that they cannot be used to fix fully saturated lipids. On the basis of existing theories concerning complex colloid systems, a fixation method was developed that allows the electron microscope study of the structure of phospholipid models, irrespective of whether they consist of saturated or unsaturated compounds. With this fixation, namely tricomplex flocculation by means of suitable ions, the structure of the lipid molecules is not altered. Moreover, the site and mode of action of this fixation are well known. The first application of this method to the study of isolated beef brain phospholipids is described.

PROPAGATION OF ACTION POTENTIALS AND THE STRUCTURE OF THE NEXUS IN CARDIAC MUSCLE

The hypothesis that the nexus is a specialized structure allowing current flow between cell interiors is corroborated by concomitant structural changes of the nexus and changes of electrical coupling between cells due to soaking in solutions of abnormal tonicity. Fusiform frog atrial fibers are interconnected by nexuses. The nexuses, desmosomes, and regions of myofibrillar attachment of this muscle are not associated in a manner similar to intercalated discs of guinea pig cardiac muscle. Indeed, nexuses occur wherever cell membranes are closely apposed. Action potentials of frog atrial bundles detected extracellularly across a sucrose gap change from monophasic to diphasic when the gap is shunted by a resistor. This indicates that action potentials are transmitted across the gap when sufficient excitatory current is allowed to flow across the gap. When the sucrose solution in the gap is made hypertonic, propagation past the gap is blocked and the resistance between the cells in the gap increases. Electron micrographs demonstrate that the nexuses of frog atrium and guinea pig ventricle are ruptured by hypertonic solutions.