Biochemical evidence for functional heterogeneity of cardiac sarcoplasmic reticulum vesicles

Two subpopulations of cardiac sarcoplasmic reticulum vesicles were resolved functionally, based on their sensitivities to the drug ryanodine. These two subpopulations of sarcoplasmic reticulum vesicles, termed ryanodine-sensitive and ryanodine-insensitive, were separated by preloading crude cardiac microsomes with Ca2+ oxalate in the presence of ATP, followed by sucrose density gradient centrifugation. Ryanodine-insensitive vesicles accumulated most of the Ca2+ oxalate during the preload, and constituted the densest subfraction recovered from the sucrose gradient. These ryanodine-insensitive vesicles exhibited the highest density of Ca2+ pumps, and accounted for 10 to 15% of the total protein in crude cardiac microsomes. Ryanodine-insensitive vesicles continued to transport substantial amounts of Ca2+ after isolation. Ryanodine-sensitive vesicles accumulated negligible Ca2+ during the preload, and were recovered from the lower density regions of the sucrose gradient. On a milligrams of protein basis, these vesicles were present in 7-fold excess over ryanodine-insensitive vesicles. Ryanodine-sensitive vesicles transported low amounts of Ca2+ under normal incubation conditions, but 3 X 10(-4) M ryanodine strikingly increased their Ca2+ uptake 5- to 10-fold. Ca2+ uptake by ryanodine-sensitive vesicles was uniquely regulated by Ca2+ ion concentration. Elevation of the ionized Ca2+ concentration from 2 to 4 microM increased Ca2+ uptake by these vesicles greater than 5-fold, but had no effect on their Ca2+-dependent ATPase activity. These ryanodine- and Ca2+ concentration-dependent effects were apparent for only ryanodine-sensitive vesicles. Sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed distinct differences in polypeptide staining between ryanodine-sensitive and ryanodine-insensitive vesicles, confirming by an independent method that the two populations of vesicles were different. These data provide the first biochemical evidence for functional and structural heterogeneity of cardiac sarcoplasmic reticulum vesicles.     

Evoked potentials,saccadic velocities,and computerized tomography in diagnosis of multiple sclerosis.

One hundred and two patients with suspected or established multiple sclerosis (MS) were investigated by one or more of the following techniques: measurement of visual evoked potentials (VEP); measurement of cervical and cortical somatosensory evoked potentials (SEP); measurement of horizontal saccadic eye movement velocities (SV); and computerised axial tomography of the cranium and orbits (CT). Each of the techniques was valuable in detecting abnormalities, some of which were subclinical, in many patients. More abnormalities were found in patients studied by more than one technique, the most being detected in patients who were studied by all five techniques. We conclude that the techniques have a complementary role in investigating suspected MS.     

H-Type Bovine Spongiform Encephalopathy: Complex Molecular Features and Similarities with Human Prion Diseases

We previously reported that some cattle affected by bovine spongiform encephalopathy (BSE) showed distinct molecular features of the protease-resistant prion protein (PrP^res) in Western blot, with a 1–2 kDa higher apparent molecular mass of the unglycosylated PrP^res associated with labelling by antibodies against the 86–107 region of the bovine PrP protein (H-type BSE). By Western blot analyses of PrP^res, we now showed that the essential features initially described in cattle were observed with a panel of different antibodies and were maintained after transmission of the disease in C57Bl/6 mice. In addition, antibodies against the C-terminal region of PrP revealed a second, more C-terminally cleaved, form of PrP^res (PrP^res #2), which, in unglycosylated form, migrated as a ≈ 14 kDa fragment. Furthermore, a PrP^res fragment of ≈7 kDa, which was not labelled by C-terminus-specific antibodies and was thus presumed to be a product of cleavage at both N- and C-terminal sides of PrP protein, was also detected. Both PrP^res #2 and ≈7 kDa PrP^res were detected in cattle and in C57Bl/6 infected mice. These complex molecular features are reminiscent of findings reported in human prion diseases. This raises questions regarding the respective origins and pathogenic mechanisms in prion diseases of animals and humans.Key Words: prion, BSE, Creutzfeldt-Jakob, Gerstmann-Sträussler-Scheinker, Western blot, amyloid     

Host origin of plastid solute transporters in the first photosynthetic eukaryotes

Background  

It is generally accepted that a single primary endosymbiosis in the Plantae (red, green (including land plants), and glaucophyte algae) common ancestor gave rise to the ancestral photosynthetic organelle (plastid). Plastid establishment necessitated many steps, including the transfer and activation of endosymbiont genes that were relocated to the nuclear genome of the 'host' followed by import of the encoded proteins into the organelle. These innovations are, however, highly complex and could not have driven the initial formation of the endosymbiosis. We postulate that the re-targeting of existing host solute transporters to the plastid fore-runner was critical for the early success of the primary endosymbiosis, allowing the host to harvest endosymbiont primary production.     

Respiratory muscle dynamics and control during exercise with externally imposed expiratory flow limitation.

To determine how decreasing velocity of shortening (U) of expiratory muscles affects breathing during exercise, six normal men performed incremental exercise with externally imposed expiratory flow limitation (EFLe) at approximately 1 l/s. We measured volumes of chest wall, lung- and diaphragm-apposed rib cage (Vrc,p and Vrc,a, respectively), and abdomen (Vab) by optoelectronic plethysmography; esophageal, gastric, and transdiaphragmatic pressures (Pdi); and end-tidal CO2 concentration. From these, we calculated velocity of shortening and power (W) of diaphragm, rib cage, and abdominal muscles (di, rcm, ab, respectively). EFLe forced a decrease in Uab, which increased Pab and which lasted well into inspiration. This imposed a load, overcome by preinspiratory diaphragm contraction. Udi and inspiratory Urcm increased, reducing their ability to generate pressure. Pdi, Prcm, and Wab increased, indicating an increased central drive to all muscle groups secondary to hypercapnia, which developed in all subjects. These results suggest a vicious cycle in which EFLe decreases Uab, increasing Pab and exacerbating the hypercapnia, which increases central drive increasing Pab even more, leading to further CO2 retention, and so forth.