The effect of cAMP on the cell membrane potential and intracellular ion activities in proximal tubule of Rana esculenta

Experiments were performed in proximal tubule of the isolated perfused frog kidney to evaluate peritubular cell membrane potentials (PDpt), and the intracellular ion activities of sodium (Nai+), chloride (Cli-) and potassium (Ki+) under control conditions and following peritubular application of dibutyryl-cyclic AMP (cAMP, 2 X 10(-4) mol X 1(-1)). Conventional and ion-sensitive microelectrodes were applied to record continuously cAMP-induced changes of these parameters in individual proximal tubule cells. Within a few minutes a significant hyperpolarisation of PDpt (delta = 2.0 +/- 0.2 mV) occurs simultaneously with a decrease of Nai+ (delta = 2.5 +/- 0.5 mmol X 1(-1)). Ki+ increases (delta = 3.6 +/- 0.9 mmol X 1(-1)) and Cli- decreases (0.4 +/- 0.07 mmol X 1(-1)) slightly, but significantly. With both ions the alterations of the chemical gradient is significantly smaller than the potential shift. PDte is not significantly altered by cAMP. The cAMP-induced hyperpolarisation of PDpt can be observed in presence and absence of luminal glucose. However, omission of Na+ from the luminal perfusate abolishes the hyperpolarising effect of cAMP on PDpt. The results suggest that cAMP reduces sodium entry from the lumen into the cell, thus hyperpolarising the cell membrane and decreasing Nai+. Persistence of sensitivity of PDpt to cAMP after omission of glucose indicates that other Na+ coupled transport processes and/or passive Na+ conductance are affected by cAMP. the changes of Ki+ and Cli- are secondary, following the change of PDpt.

Effect of luminal potassium on cellular sodium activity in the early distal tubule of Amphiuma kidney

From previous studies it is known that a furosemide-sensitive sodium chloride cotransport system is operative in the luminal cell membrane of the early distal amphibian tubule. Since inhibition of sodium chloride cotransport prevents potassium reabsorption in this nephron segment, experiments were carried out to evaluate further the possible relationship between sodium chloride and potassium transport by studying the changes of cellular sodium activity following luminal deletion of potassium ions. Sodium-sensitive liquid ion exchange microelectrodes and conventional microelectrodes were employed to determine the transepithelial potential (PDte), the peritubular cell membrane potential (PDpt) and the intracellular sodium activity (Nai+) in the presence and absence of luminal potassium. The ratio of the luminal cell membrane resistance over the peritubular cell membrane resistance (Rlu/Rpt) was also estimated. When potassium ions are omitted from the luminal perfusate, PDpt hyperpolarizes by some 20 mV, PDte approaches zero and Nai+ decreases by about 40%. Rlu/Rpt is more than doubled in the presence of a potassium-free perfusate. Both potential and resistance changes are fully reversible. Similar results were obtained in experiments in which Barium ions (1 mmol/1 BaCl2) were present during the luminal potassium substitution. Our results indicate that absence of potassium inhibits luminal sodium chloride entry; as a result of continued peritubular sodium extrusion cellular sodium activity falls. The increase of Rlu/Rpt following perfusion with a potassium-free perfusate is interpreted as a decrease of a significant electrodiffusive potassium conductance in the luminal cell membrane.

Cellular Mechanism of the furosemide sensitive transport system in the kidney

Experiments were performed in the distal tubule of the doubly-perfused kidney of Amphiuma to determine active and passive forces, involved in the transport processes of potassium, sodium and chloride. Ion-sensitive microelectrodes and conventional microelectrodes were applied to estimate intracellular ion activities, cell membrane potentials and net flux of potassium and chloride under control conditions and during inhibition of active transport. Sodium chloride cotransport, located in the luminal cell membrane is postulated, based on the following observations: Total omission of sodium from the tubular lumen inhibits furosemide sensitive chloride reabsorption, decreases the lumen positive transepithelial potential difference and leads to a dramatic decrease of intracellular chloride. The experiments further suggest that potassium ions are involved in the sodium chloride transport system because potassium reabsorption is inhibited by furosemide and because intracellular sodium falls significantly when potassium ions are removed from the tubular fluid. Furthermore, there is experimental evidence that the luminal potassium uptake mechanism is suppressed after potassium adaptation. Under these conditions potassium transport is found to be insensitive to furosemide. The data suggest a furosemide sensitive cotransport system for sodium, chloride and potassium, operative in the luminal cell membrane. The energy for this carrier-mediated transport process is provided by the large "downhill" gradient of sodium across the luminal cell membrane which is maintained by the sodium pump located in the peritubular cell membrane.

Microvasculature of human colorectal epithelial tumors. An electron microscopic study

The ultrastructure of the microvasculature in human colorectal adenomas and carcinomas was studied, and compared with that of normal tissue. Blood vessels in adenomas were generally of normal structure, whereas carcinoma vessels displayed a variety of structural alterations. Endothelial proliferation was frequently observed in all the eleven carcinomas examined, which confirms the reports of new vessel formation in experimental malignant tumors. The presence of fenestrations in obviously abnormal endothelium was tentatively attributed to hypoxia, vascular regression or immaturity of the cells, in spite of the fact that normal capillaries in colonic mucosa are fenestrated. Some vessels showed multilayered basement membranes, various types of activated cells containing numerous lysosomal granules, and thickened perivascular tissue. These features may be a vascular response to repeated damage or a manifestation of vascular remodelling. Dilated thin-walled vessels, which were usually found at the periphery of carcinomas, were identified as venules. Small vessels located between the closely apposed carcinoma tubules were not obviously abnormal. They were nevertheless considered to be tumor-induced vessels which had undergone differentiation. The differences in vascular morphology between adenomas and carcinomas were considered to be due to their different growth patterns, growth rates and degrees of maturity.

Effects of inhibition of chloride transport on intracellular sodium activity in distal amphibian nephron

Previous experiments had demonstrated that cell chloride activities in early distal tubule cells of Amphiuma are above equilibrium distribution. Chloride activities fell sharply towards electrochemical equilibrium following perfusion of the tubular lumen with furosemide or with sodium-free solutions. These results suggested a furosemide-sensitive sodium chloride cotransport system in the luminal cell membrane. The present experiments were carried out to evaluate directly the electrochemical driving forces acting on sodium ions under similar experimental conditions. Intracellular sodium activity measurements were performed in the doubly-perfused kidney of Amphiuma by means of single-barreled liquid ion-exchange microelectrodes. Basolateral cell membrane potential and resistance ratio measurements of tubular cell membranes were also carried out under control conditions and after inhibition of chloride transport by luminal application of furosemide (5 . 10(-5) mol/l) or by omission of chloride. Control conditions were characterized by a steep downhill electrochemical gradient for sodium ions from lumen to cell. Inhibition of chloride transport led to a sharp decrease of intracellular sodium activity and to hyperpolarization of the peritubular membrane potential while the resistance ratio of the tubular cell membranes did not change significantly. These results demonstrate the presence of low cellular sodium activities in early distal tubule cells. The sharp decline of cell sodium after furosemide and after luminal chloride removal is consistent with inhibition of a sodium chloride cotransport system and continued peritubular sodium extrusion. The latter can increase the electrochemical gradient of sodium ions beyond that observed under control conditions.

The free forearm flap--a report of 25 cases

In 25 cases using microvascular techniques, free forearm flaps were used for reconstruction of various tissue defects. 15 flaps were used for repair of hand injuries, 5 for facial defects, 1 for lower extremity deformity and 4 for total rhinoplasty. All flaps survived. The arterial blood supply of the forearm flap comes from the cutaneous branches of the radial artery while its venous drainage is via cephalic vein and the radial comitantes veins. The forearm flap has a thin layer of subcutaneous fatty tissue, can provide quite large area of soft tissue and the vascular pedicle is long with moderately large calibre vessels. The donor area, however, has to be skin grafted, leaving an unsightly scar over the forearm which is one of the shortcomings of this flap. Secondly it means sacrificing a major arterial supply to the hand on the donor side.

Hereditary elliptocytosis: morphologic abnormalities during acute hepatitis

A 10-year-old black girl with hereditary elliptocytosis had a transient increase in hemolysis and unusual red cell morphologic changes during an episode of acute hepatitis. Changes in membrane lipids of these elliptocytes with defective membrane skeletal protein and abnormal distribution of cholesterol may be responsible for this phenomenon.

Evans syndrome in childhood

The combination of idiopathic thrombocytopenic purpura and autoimmune hemolytic anemia is rare in childhood. Among 164 instances of ITP and 15 instances of AHA, 11 patients were found to have this combination. Three were found to have systemic lupus erythematosus, one had aplastic anemia, and seven had Evans syndrome. Neutropenia, at times associated with bacterial infections, occurred in four of the latter patients. Unlike most cases of ITP or AHA in childhood, the clinical course of Evans syndrome is usually chronic and relapsing. Treatment including corticosteroids, splenectomy, and immunosuppressive agents has been generally unsatisfactory. In view of the frequent presence of antibodies directed at red blood cells, platelets, neutrophils, and lymphocytes, immunopancytopenia may be a better term for this condition.

Three new yellow loci in Chlamydomonas reinhardtii

Three phenotypically 'yellow', mendelian mutants of Chlamydomonas reinhardtii have been isolated and tested for allelism with the yellow mutant y-1 a1 and with each other. The three mutants represent three new yellow loci, two of which are located on linkage group I. Like y-1a, the mutants accumulate protochlorophyllide when grown under dim light, but have a wildtype phenotype when grown in the light. We conclude that the control of light-independent protochlorophyllide reduction is more complex than has been thought previously.

Free transfer of the second toe combined with dorsalis pedis flap using microvascular technique for reconstruction of the thumb and other fingers

The blood supply to the dorsum of the feet was studied in 100 cadaver feet specimens. The understanding of anatomical variation of branches of dorsalis pedis artery and its venous system are important in determining the success of the operation for free toe or dorsalis pedis flap transplantation. Three groups of fine branches of arterial system supplying the skin on the dorsum of the feet are classified; the central, the intermediate and the marginal groups. The central group is the dorminant blood supply to the dorsalis pedis skin flap. The first dorsal metatarsal artery which is a main branch of the dorsalis pedis artery remains to be dominant feeding artery to the second toe. From these cadaver specimens, three types of distribution are formulated, but with different percentages of distribution as compared with that of Gilbert's data. Seven consecutive cases of the second toe combined with dorsalis pedis flap transfer using microvascular technique for the reconstruction of thumb and other fingers are reported. The operation is designed to meet the demand of one stage reconstruction of the missing thumb or other fingers which are associated with surrounding soft tissue defects. Preparatory soft tissue repair by skin flap or tube flap is thus obviated.

Genetic control of chlorophyll biosynthesis in chlamydomonas: analysis of a mutant affecting synthesis of delta-aminolevulinic acid

A Mendelian mutation, r-1, in Chlamydomonas reinhardtii has been isolated which elevates protoporphyrin accumulation of the Mendelian protoporphyrin mutants brS-1 and brC-1 more than 20 fold. This increased protoporphyrin accumulation is shown to result from increased delta-aminolevulinic acid synthesis in the double mutants brS-1 r-1 and brC-1 r-1 over that of brS-1 and brC-1 alone. By itself, the r-1 mutation has no detectable protoporphyrin accumulation and has reduced levels of delta-aminolevulinic acid synthesizing activity, chlorophyll, protoheme, and cytochrome oxidase activity. The low levels of chlorophyll and protoheme in r-1 can be increased by feeding delta-aminolevulinic acid. We hypothesize that r-1 may be a mutation of the gene coding for the delta-aminolevulinic acid synthesizing enzyme which reduces the sensitivity of this enzyme to feedback inhibition by protoporphyrin or heme as well as reducing the overall activity of the enzyme. Evidence is also presented for a single delta-aminolevulinic acid synthesizing enzyme serving both chlorophyll and heme biosynthesis.

Encephalopathy associated with occult neuroblastoma

✓ The authors report four cases of occult neuroblastoma in children with the striking clinical findings of opsoclonus, myoclonus, and ataxia. The diagnostic value of plain roentgenograms of the chest and abdomen or an intravenous pyelogram is emphasized. Assays for vanillyl mandelic acid and cystathionine may be of value. The clinical course and pathogenesis of encephalopathies due to neuroblastoma are discussed.