Permeability of sarcoplasmic reticulum membrane. The effect of changed ionic environments on Ca2+ release

Summary Permeability properties and the effects of a changed membrane potential on Ca²⁺ release of sarcoplasmic reticulum vesicles of rabbit skeletal muscle were investigated by Millipore filtration. The relative permeability of sarcoplasmic reticulum to solutes determined under conditions of isotope exchange at equilibrium and/or under conditions of net flow of solute and water into the vesicles was as follows: sucrose, Ca²⁺, Mn²⁺–, choline⁺, Tris⁺–+, Na⁺, Li⁺, Cl^–. Transient membrane potentials were induced by rapidly changing the ionic environment of the vesicles. Knowledge of the relative permeation rates of the above ions allowed prediction of the direction and extent of membrane polarization. Osmotic effects in the polarization measurements due to the rapid influx of solute and water into the vesicles were minimized by using media containing a fast (K⁺ or Cl^–) and a relatively slow (gluconate^– or choline⁺) penetrating ion.⁴⁵Ca²⁺ efflux from vesicles derived from different parts of the sarcoplasmic reticulum structure was not appreciably changed when vesicles were made more positive inside (choline chloride potassium gluconate) or more negative inside (potassium gluconate choline chloride). These studies suggest that part or all of the ion-induced changes in sarcoplasmic reticulum membrane permeability, previously interpreted to indicate depolarization-induced Ca²⁺ release, may be due to osmotic effects.     

The synthesis and biological activity of Ala3,14-somatostatin

The tetradecapeptide H-Ala-Gly-Ala-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-Ala-OH (Ala³, 14-somatostatin) an analog of the somatotropin release inhibiting factor (somatostatin SRIF) was synthesized by solid phase peptide methods. It shows somatotropin release inhibiting activity $\text{in vitro}$ at 5 μg/ml concentration.     

Solvent removal during synthetic and Nephila fiber spinning

The process by which spiders make their mechanically superior fiber involves removal of solvent (water) from a concentrated protein solution while the solution flows through a progressively narrowing spinning canal. Our aim was to determine a possible mechanism of spider water removal by using a computational model. To develop appropriate computational techniques for modeling of solvent removal during fiber spinning, a study was first performed using a synthetic solution. In particular, the effect of solvent removal during elongational flow (also exhibited in the spinning canal of the spider) on fiber mechanical properties was examined. The study establishes a model for solvent removal during dry spinning of synthetic fibers, assuming that internal diffusion governs solvent removal and that convective resistance is small. A variable internal solvent diffusion coefficient, dependent on solvent concentration, is also taken into account in the model. An experimental setup for dry (air) spinning was used to make fibers whose diameter was on the order of those made by spiders (approximately 1 microm). Two fibers of different thickness, corresponding to different spinning conditions, were numerically modeled for solvent removal and then mechanically tested. These tests showed that the thinner fiber, which lost more solvent under elongational flow, had 5-fold better mechanical properties (elastic modulus of 100 MPa and toughness of 15 MJ/m3) than the thicker fiber. Even though the mechanical properties were far from those of dragline spider silk (modulus of 10 GPa and toughness of 150 MJ/m3), the experimental methodology and numerical principles developed for the synthetic case proved to be valuable when establishing a model for the Nephila spinning process. In this model, an assumption of rapid convective water removal at the spinning canal wall was made, with internal diffusion of water through the fiber as the governing process. Then the diffusion coefficient of water through the initial spinning solution, obtained ex vivo from the Nephila clavipes major ampullate gland, was determined and incorporated into the numerical procedure, along with the wall boundary conditions and canal geometry. Also, a typical fiber reeling speed during web making, as well as the assumption of a dry exiting fiber, were included in the model. The results show that a cross-section of spinning solution (dope), which is initially 70% water, spends 19 s in the spinning canal in order to emerge dry. While the dope cross-section traverses the canal, its velocity increases from 0.37 mm/s at the entrance to 12.5 mm/s at the canal exit. The obtained results thus indicate that simple diffusion, along with the dry wall boundary condition, is a viable mechanism for water removal during typical Nephila fiber spinning.     

Injury and short term mortality of benthic stream fishes – a comparison of collection techniques

Small benthic fish such as darters are frequently collected for stream inventory purposes or to document habitat use, with the intent of releasing the fish unharmed following enumeration. The purpose of this study was to examine the injury and short term mortality (8 d) of greenside darters captured by live wire pot trapping and electrofishing, using two different settings (80Hz, 6ms and 60Hz, 6ms). Two different electrofishing techniques were used, spot electrofishing and sweep electrofishing. Short term mortality was highest for fish collected in live pot traps. Abrasion from the wire traps appeared to remove scales and irritate the skin. By the conclusion of the study, 74% of the fish caught in live pot traps were dead from fungal lesions. Greenside darters captured by all electrofishing methods exhibited low short term mortality (< 10%). The only initial mortality, hemorrhaging and spinal damage, occurred for fish collected using 80Hz, 6ms sweep technique, although the short term mortality was still far less than that observed among trapped fish. The spot electrofishing technique resulted in no injury, with either of the settings. Live trapping produces little initial mortality, and thus may be wrongly viewed as a safe alternative for the collection of threatened benthic stream fishes, compared to electrofishing. We suggest that researchers studying small fish in warmwater systems use caution when collecting and handling fish for subsequent release. This revised version was published online in July 2006 with corrections to the Cover Date.     

The brain renin-angiotensin system: location and physiological roles

Angiotensinogen, the precursor molecule for angiotensins I, II and III, and the enzymes renin, angiotensin-converting enzyme (ACE), and aminopeptidases A and N may all be synthesised within the brain. Angiotensin (Ang) AT(1), AT(2) and AT(4) receptors are also plentiful in the brain. AT(1) receptors are found in several brain regions, such as the hypothalamic paraventricular and supraoptic nuclei, the lamina terminalis, lateral parabrachial nucleus, ventrolateral medulla and nucleus of the solitary tract (NTS), which are known to have roles in the regulation of the cardiovascular system and/or body fluid and electrolyte balance. Immunohistochemical and neuropharmacological studies suggest that angiotensinergic neural pathways utilise Ang II and/or Ang III as a neurotransmitter or neuromodulator in the aforementioned brain regions. Angiotensinogen is synthesised predominantly in astrocytes, but the processes by which Ang II is generated or incorporated in neurons for utilisation as a neurotransmitter is unknown. Centrally administered AT(1) receptor antagonists or angiotensinogen antisense oligonucleotides inhibit sympathetic activity and reduce arterial blood pressure in certain physiological or pathophysiological conditions, as well as disrupting water drinking and sodium appetite, vasopressin secretion, sodium excretion, renin release and thermoregulation. The AT(4) receptor is identical to insulin-regulated aminopeptidase (IRAP) and plays a role in memory mechanisms. In conclusion, angiotensinergic neural pathways and angiotensin peptides are important in neural function and may have important homeostatic roles, particularly related to cardiovascular function, osmoregulation and thermoregulation.     

Effects of Acid on Plant Litter Decomposition in an Arctic Lake

The effects of acid on the microbial decomposition of the dominant aquatic macrophyte (Carex sp.) in Toolik Lake, Alaska were studied in microcosms during the ice-free season of 1980. Toolik Lake is slightly buffered, deep, and very oligotrophic. Microbial activities, as determined by ¹⁴C-acetate incorporation into extractable lipids, associated with Carex litter were significantly (P < 0.01) reduced within 2 days at pHs of 3.0 and 4.0, but not 5.0, 5.5, or 6.0, as compared with ambient controls (pH 7.4). ATP levels were significantly reduced at pH 3.0, but not at the other pHs tested. After 18 days, microbial activity significantly correlated with weight loss (P < 0.05), nitrogen content (P < 0.01), and C/N ratios (P < 0.01) of the litter, but did not correlate with ATP levels. Scanning electron microscopy of the litter surface revealed that the fungi present at ambient pH did not become dominant at pHs below 5.5, diatoms were absent below pH 4.0, and bacterial numbers and extracellular slime were greatly reduced at pH 4.0 and below. Mineralization of Carex¹⁴C-lignin-labeled or ¹⁴C-cellulose-labeled lignocellulose was reduced at pH 2.0, but not at pH 4.0, 5.0, or 6.0, compared with controls (pH 7). We concluded that if the pH of the water from this slightly buffered lake was sufficiently reduced, rates of litter decomposition would be significantly reduced.     

Accelerated hand bone mineral density loss is associated with progressive joint damage in hands and feet in recent-onset rheumatoid arthritis

Introduction

To investigate whether accelerated hand bone mineral density (BMD) loss is associated with progressive joint damage in hands and feet in the first year of rheumatoid arthritis (RA) and whether it is an independent predictor of subsequent progressive total joint damage after 4 years.

Methods

In 256 recent-onset RA patients, baseline and 1-year hand BMD was measured in metacarpals 2-4 by digital X-ray radiogrammetry. Joint damage in hands and feet were scored in random order according to the Sharp-van der Heijde method at baseline and yearly up to 4 years.

Results

68% of the patients had accelerated hand BMD loss (>-0.003 g/cm²) in the first year of RA. Hand BMD loss was associated with progressive joint damage after 1 year both in hands and feet with odds ratios (OR) (95% confidence intervals [CI]) of 5.3 (1.3-20.9) and 3.1 (1.0-9.7). In univariate analysis, hand BMD loss in the first year was a predictor of subsequent progressive total joint damage after 4 years with an OR (95% CI) of 3.1 (1.3-7.6). Multivariate analysis showed that only progressive joint damage in the first year and anti-citrullinated protein antibody positivity were independent predictors of long-term progressive joint damage.

Conclusions

In the first year of RA, accelerated hand BMD loss is associated with progressive joint damage in both hands and feet. Hand BMD loss in the first year of recent-onset RA predicts subsequent progressive total joint damage, however not independent of progressive joint damage in the first year.     

Return migration of Atlantic Salmon in the River Tana: Phases of migratory behaviour

From a total of 174 multi-sea-winter Atlantic salmon radio tagged in the Tanafjord (northern Norway, 70°N) during 1992 and 1993, 48 Atlantic salmon were followed from entering the River Tana until spawning. Three phases were identified: (1) migratory, direct or stepwise migration to, or close to the position held at spawning; (2) search, movements both up and down river at or close to the position held at spawning; (3) holding, a period without movements prior to spawning. During the migratory phase, Atlantic salmon migrated directly to near the spawning area, or stopped between one and nine shorter periods during the upstream migration. Number of stops increased with increasing migratory distance in 1993, but no such correlation was found in 1992. The highest migratory speeds were recorded in the lower parts of the river. A distinct change in migratory pattern was found in 67% of the Atlantic salmon near or at the area held at spawning. Most common was a search phase of erratic movements with more than one down river movement. After the movement terminated, 96% of the Atlantic salmon had a period when no or little movement was recorded until spawning (on average 55 days in 1992 and 51 days in 1993). There was no preference for staying at, up or down river from the spawning area during this holding period. Early ascending Atlantic salmon migrated to spawning areas further from the mouth than the later arriving Atlantic salmon in 1993, but not in 1992. The proportion of time spent on the migratory phase increased, while the proportion of time spent on the holding phase decreased with increasing distance to the spawning area.