Regulation of cerebrospinal fluid potassium by the cat choroid plexus

1. The regulation of cerebrospinal fluid (c.s.f.) potassium concentration was studied using the cat choroid plexus isolated in a chamber in situ. 2. Hyperkalaemia (plasma potassium concentration greater than 6 m-equiv/l.) caused relatively small increases in c.s.f. potassium concentration. 3. Alterations in c.s.f. potassium concentration (c.s.f. K = 0-15 or 6-56 m-equiv/l.) were countered by changes in potassium concentration of the produced fluid or in the rate of potassium transport which returned c.s.f. potassium towards normal. 4. The data indicate that potassium concentration in c.s.f. secreted by the choroid plexus is actively regulated by the plexus whether the primary alteration in potassium occurs in plasma or c.s.f.     

Biopterin derivatives in human body fluids and tissues

Levels of biopterin derivatives in urine, serum, milk, cerebrospinal fluid, brain, and liver have been measured with the Crithidia fasciculata assay. Normal levels in serum and urine have been given and compared with those in a number of benign and malignant proliferative disorders, phenylketonuria, kidney disease, Parkinson's disease, schizophrenia, controlled epilepsy, rheumatoid arthritis, and pernicious anaemia. The active component of Crithidia factor in serum was 7,8-dihydrobiopterin. Tissue, urine, and some serum samples contained two active materials, the principal one being 7,8-dihydrobiopterin; a minor constituent was probably tetrahydrobiopterin. Serum biopterin levels following methotrexate administration were raised and subsequent administration of folic acid and 5-formyltetrahydrofolic acid further increased serum levels of biopterin derivatives; this was in contrast to the total absence of response to oral folates without prior methotrexate and to 5-methyltetrahydrofolic acid either with or without methotrexate being given.     

Response of Neisseria gonorrhoeae to Bdellovibrio species

We have previously proposed that if the two half-layers of a membrane are different in their protein and lipid compositions, they may respond differently to some membrane perturbation (the bilayer couple hypothesis). This hypothesis has been applied to explain the changes in shape of human erythrocytes that are produced by a variety of amphipathic compounds. These compounds are presumed to intercalate by their hydrophobic ends into the lipid portions of the membrane; if the compounds are anions, the binding is preferentially to the outer half of the bilayer, if cations, to the inner half. It is proposed that such preferential binding causes an expansion of one half-layer relative to the other, with a corresponding change in cell shape. The predicted sidedness of these shape changes is now demonstrated in experiments with methochlorpromazine and 2,4,6-trinitrophenol. Under appropriate nonequilibrium or equilibrium or equilibrium conditions, both of these compounds are shown to be either crenators or cup-formers of the intact erythrocyte, depending upon which side of the membrane they are concentrated in. These results therefore strongly support the bilayer couple hypothesis.     

N(3) soordination by a purine analog. The crystal structure of trichloro(8-azaadeninium)zinc(II)

Duplication of the straight sinus is often noted in the venous phase of carotid angiograms. Since this vascular anomaly is rarely described in the literature, the authors present its incidence in a series of 700 cases, and consider its embryological origins and clinical significance.     

Synthesis in vitro of intrinsic membrane proteins by free, membrane-bound, and Golgi apparatus-associated polyribosomes from rat liver

A fraction of intrinsic membrane proteins was prepared from the major membranous cell components of rat liver by extraction of the membranes with KCl and deoxycholate. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the compositions of the intrinsic protein fractions from rough and endoplasmic reticulum, smooth endoplasmic reticulum. Golgi apparatus, plasma membrane, and nuclear envelope were similar to each other but distinct from that of mitochondria. Among endomembranes, differences were in the ratios of protein constituents plus a few protein bands of Golgi apparatus and plasma membranes not found in endoplasmic reticulum or nuclear envelope. The abilities of total rough endoplasmic reticulum, polysomes released from rough endoplasmic reticulum, and free polysomes to incorporate amino acids into the intrinsic protein fraction were tested in vitro. Polysomes bound to endoplasmic reticulum has the greatest capacity to synthesize proteins of this fraction as shown by co-purification of radioactive products and by immunoprecipitation. Although the majority of the radioactive products synthesized by bound polysomes were distinct from those synthesized by free polysomes, certain radioactive products synthesized by free polysomes also co-purified with intrinsic membrane proteins. The results show no absolute segregation between free and bound polysomes in the synthesis of intrinsic membrane proteins. However, the majority of these proteins appear to be synthesized by polysomes bound to the endoplasmic reticulum. Several intrinsic proteins found in plasma membranes do not appear in rough endoplasmic reticulum. To determine where these proteins were synthesized, the ability of other endomembrane components to support in vitro incorporation of [14C]leucine into protein was examined. In contrast to plasma membranes, isolated Golgi apparatus fractions did incorporate [14C]leucine to an extent greater than could be explained by contamination with rough endoplasmic reticulum. Golgi apparatus in situ and isolated from rat liver have polyribosomes associated with a zone of cytoplasm at the Golgi apparatus periphery occupied by tubules and vesicles. The polysomes are not directly attached to membranes as with rough endoplasmic reticulum and may represent a special class of "Golgi apparatus-associated" polysomes. The polysomes, when associated with Golgi apparatus membranes, incorporated amino acids in vitro. The products synthesized in vitro were analyzed by treatment with KCl and deoxycholate and separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Certain proteins synthesized by the Golgi apparatus-associated polysomes remained insoluble after the treatment with KCl and deoxycholate. The proteins synthesized by the Golgi apparatus fraction had mobilities similar to proteins in plasma membranes which were absent from endoplasmic reticulum, and which were relatively minor components of Golgi apparatus...