Berit I. Kristensen

Electron microscopy of filaments in the basal part of rat kidney tubule cells, and their in situ interaction with heavy meromyosin

SummaryBy electron microscopy, the prominent bundles of filaments occurring in the basal part of proximal and distal tubule cells and in interstitial cells of rat kidney cortex were studied in cells fixed by vascular perfusion, in glycerol-extracted cells and in glycerol-extracted cells treated with heavy meromyosin (HMM).The studies of perfusion-fixed tissue showed that the proximal tubule cells contained in their most basal part filamentous bundles oriented transversely around the tubule. The bundles consisted of trightly packed thin filaments (50–80 Å in diameter). Similar but less prominent bundles were found in distal tubule cells and in interstitial cells. The dimension of these filaments was similar to that of actin filaments and their insertion in the basal cell membrane of the tubule epithelial cells resembled the insertion of actin filaments in the cell membrane of smooth muscle cells.The studies on glycerol-extracted cells revealed that some tubule cells contained two types of filaments (60–80 Å and 130–170 Å in diameter) located side by side in the basal filamentous bundles. The dimension of the thick filaments corresponds well to the values for myosin filaments in glycerinated smooth and skeletal muscle.The studies on HMM-reacted renal tissue revealed that the thin filaments (60–80 Å) described in tubule and interstitial cells are probably actin filaments, as they formed characteristic arrowhead complexes morphologically indistinguishable from the complexes of HMM with actin filaments in smooth and striated muscle cells.Our results provide strong evidence that a two-filament contractile system, based on interaction of actin and myosin filaments, exists in renal tubule and interstitial cells. As a hypothesis it is proposed that it is changes in tonus of the basal filamentous system in the proximal tubule cells which stabilize the intratubular pressure, possibly via angiotensin.

The human red cell voltage-regulated cation channel. The interplay with the chloride conductance, the Ca(2+)-activated K(+) channel and the Ca(2+) pump.

The activation/deactivation kinetics of the human erythrocyte voltage-dependent cation channel was characterized at the single-channel level using inside-out patches. It was found that the time dependence for voltage activation after steps to positive membrane potentials was slow (t1/2 about 30 s), whereas the deactivation was fast (t1/2 about 15 ms). Both activation and deactivation of this channel were also demonstrated in intact red cells in suspension. At very positive membrane potentials generated by suspension in extracellular low Cl− concentrations, the cation conductance switched on with a time constant of about 2 min. Deactivation of the cation channel was clearly demonstrated during transient activation of the Gárdos channel elicited by Ca2+ influx via the cation channel and ensuing efflux via the Ca2+ pump. Thus, the voltage-dependent cation channel, the Gárdos channel and the Ca2+ pump constitute a coupled feedback-regulated system that may become operative under physiological conditions.

A two-filament system and interaction of heavy meromyosin (HMM) with thin filaments in smooth muscle

SummaryThe structure of glycerinated smooth muscle from small intestine of adult rat was investigated by electron microscopy. In the central parts of the tissue blocks a two-filament system was found, consisting of parallel thick and thin filaments with regularly spaced interconnections, closely resembling that of striated muscle. In the peripheral parts of the blocks only thin filaments were found. The thin filaments were identified as actin by the formation of arrowhead complexes after incubation with heavy meromyosin.

Behavioural modification of the optic tentacle of Helix pom atia; effect of puromycin, activity of S-100

1. 1. A long-term learning phenomenon in the tentacle of Helix pomatia has been observed. 2. 2. Repeated mechanical stimulation of the optic tentacle led to habituation of the associated withdrawal-extension action pattern whereas repeated combined mechanical and electrical stimulation potentiated the reflex. 3. 3. The potentiation was present 40 days after four sessions of stimulations. Sessions spaced with proportionally increasing intervals were more effective than massed training. Puromycin (125 mg/ml) blocked 80% of protein synthesis as well as the long-term but not the short-term retention of potentiation. 4. 4. Contrary to observations in other preparations, the amount of water soluble proteins, notably S-100, was not affected by learning. Injections in vivo of and exposure of brain in vitro to S-100 had no effect on learning or a variety of brain potentials.

Variations in myoneme birefringence in relation to length changes in Stentor coeruleus.

Abstract The stalk segment of the heterotrich ciliate, Stentor coeruleus , appears nearly isotropic in the contracted state and develops a characteristic birefringence during extension. The birefringence occurs in stripes and is associated with the myonemes, one of the two longitudinally running subpellicular fiber systems. Electron microscopical investigations reveal changes in the ultrastructure of the myonemes from the extended to the contracted state. The relaxed myonemes consist mainly of 3 nm filaments running in the longitudinal direction, while the contracted myonemes show 10 nm tubular-like filaments, more randomly oriented. It is suggested that during elongation the randomly oriented tubular filaments undergo a conformational change to more regularly arranged thin filaments, thus causing development of birefringence.

Incorporation of tyrosine into the rubber-like cuticle of locusts studied by autoradiography

Abstract Incorporation of l -tyrosine, generally labelled with tritium and given as a single injection into the haemolymph, is shown to take less than 6 hr, and the lag-phase is less than 1–2 hr. The brightly fluorescent bands in resilin are synthesized during the day periods, whereas the faintly fluorescent bands are synthesized during the night periods. It is shown that the part of the prealar arm where two chitin lamellae are missing is synthesized soon after emergence.

Annexins from Ehrlich ascites cells inhibit the calcium-activated chloride current in Xenopus laevis oocytes

Abstract The effect of annexins II, III and V, purified from different species, on the calcium-activated chloride current across the stage-V to stage-VI Xenopus laevis oocyte membrane was tested either directly, using calcium entry mediated by depolarization, by A23187 permeabilization of oocytes or indirectly by quisqualate stimulation of a metabotropic glutamate receptor in the membrane expressed by the oocyte after injection of mRNA. The annexins isolated from the Ehrlich ascites cell, which is a mouse tumor cell, were found to be potent inhibitors of the chloride current, showing half-maximal inhibition at 50 nM, whereas no block was found using bovine or porcine annexins isolated from lung tissue. Of the annexins tested, we found annexin III to be naturally occurring in the oocyte, while only trace amounts of annexins II and V could be demonstrated. The inhibition pattern varied somewhat according to the stimulus method, the inhibition being more complete when an indirect stimulus via the metabotropic receptor was applied compared to a direct calcium stimulus.

Sialic acid, electrophoretic mobility and transmembrane potentials of the Amphiuma red cell.

Red cells from the giant salamander Amphiuma means are shown to contain sialic acid. The amount removed by the action of neuraminidase is equal to that released by acid hydrolysis, indicating that all of the sialic acid is present on the outer surface of the plasma membrane. These cells have a negative electrophoretic mobility and 100% enzymatic removal of sialic acid results in a 40% reduction in the mobility, suggesting that either a fraction of the sialic acid carboxyl groups are unavailable to the action of external electric fields, or other negatively charged groups contribute to the surface charge. A further reduction in mobility of normal and sialic acid-free cells is caused by an increased extracellular calcium concentration. The negative groups affected by calcium are most likely to be phosphate groups, since the isoelectric point of the cells is found to lie between the pK values for H2PO-4 groups and the carboxyl groups of sialic acid. Membrane potentials of single cells, from which 80% or more of the total sialic acid had been removed, were identical to those measured in normal cells, confirming that sialic acid plays little, if any, direct role in the maintenance of membrane potentials and ionic permeabilities.

Identification of the major annexins in Ehrlich ascites tumor cells

1. Three calcium-binding proteins have been purified from Ehrlich ascites tumor cells. 2. They were identified by amino acid sequence analysis on selected fragments obtained by tryptic digestion. 3. The proteins belong to the annexin family and were identified as annexins II, III and V. 4. Antibodies raised against the proteins were used to examine for their presence in a number of murine tissues. 5. The occurrence was found to be in reasonable accordance with earlier reports.

Time course of incorporation of tyrosine into rubber-like cuticle of locusts

Abstract Two to 3 days after the final ecdysis adult desert locusts were injected with a single dose of tritium-labelled tyrosine and its incorporation into resilin and resilin-secreting cells was studied as a function of time by means of autoradiography. The cells appear to be uniformly labelled after only 7 min. After 20 to 30 min there is a concentration of grains at the apical border and an indication of label in the newly secreted resilin. After 45 min the secretion of resilin reaches a peak. After 5 hr the cells and therefore the haemolymph are almost free of radioactivity.