Differential control of band 3 lateral and rotational mobility in intact red cells.

Measurements of integral membrane protein lateral mobility and rotational mobility have been separately used to investigate dynamic protein--protein and protein-lipid interactions that underlie plasma membrane structure and function. In model bilayer membranes, the mobilities of reconstituted proteins depend on the size of the diffusing molecule and the viscosity of the lipid bilayer. There are no direct tests, however, of the relationship between mechanisms that control protein lateral mobility and rotational mobility in intact biological membranes. We have measured the lateral and rotational mobility of band 3 in spectrin-deficient red blood cells from patients with hereditary spherocytosis and hereditary pyropoikilocytosis. Our data suggest that band 3 lateral mobility is regulated by the spectrin content of the red cell membrane. In contrast, band 3 rotational mobility is unaffected by changes in spectrin content. Band 3 lateral mobility and rotational mobility must therefore be controlled by different molecular mechanisms.     

The distribution of erythrocyte phospholipids in hereditary spherocytosis demonstrates a minimal role for erythrocyte spectrin on phospholipid diffusion and asymmetry

In the human erythrocyte membrane phosphatidylcholine and sphingomyelin reside mainly in the outer leaflet, whereas the aminophospholipids, phosphatidylethanolamine and phosphatidylserine, are mainly found in the inner leaflet. Maintenance of phospholipid asymmetry has been assumed to involve interactions between the aminophospholipids and the membrane skeleton, in particular spectrin. To investigate whether spectrin contributes to maintaining the phospholipid transbilayer distribution and kinetics of redistribution, we studied erythrocytes from hereditary spherocytosis patients whose spectrin levels ranged from 34% to 82% of normal. The phospholipid composition and the accessibility of membrane phospholipids to hydrolysis by phospholipases were in the normal range. Spin-labeled phosphatidylserine and phosphatidylethanolamine analogues that had been introduced into the outer leaflet were rapidly transported at 37 degrees C to the inner leaflet, whereas the redistribution of spin-labeled phosphatidylcholine was slower. The kinetics of transbilayer movement of these spin-labeled phospholipid in all samples was in the normal range and was not affected by the level of spectrin. Although these erythrocyte membranes contained as little as 34% of the normal level of spectrin and were characterized by several physical abnormalities, the composition, distribution, and transbilayer kinetics of the phospholipids were found to be normal. We therefore conclude that spectrin plays, at best, only a minor role in maintaining the distribution of erythrocyte membrane phospholipid.     

Aquaporin-1 is expressed by vascular smooth muscle cells and mediates rapid water transport across vascular cell membranes

The aquaporins are a rapidly expanding family of highly conserved proteins which function as transmembrane water channels. We have previously shown that the gene for aquaporin-1 (AQP-1) is expressed in rat, aortic vascular smooth muscle cells (VSMCs) implying a specific role for AQP-1 in vascular function. In this study we set out to document the expression of AQP-1 in human arteries and found mRNA and protein in normal endothelial and VSMCs of human arteries and capillaries and in a subset of VSMCs in human atherosclerotic plaques. Secondly, we examined the regulation of AQP-1 gene expression during vascular development and following vascular injury. Studies in the rat demonstrated that AQP-1 mRNA is induced in the neonatal aorta at week 2 of postnatal development and that the protein is present in neointimal VSMCs following balloon injury. Finally, by measuring the rate of change in cell size induced by changes in external osmolarity and demonstrating that water transport can be inhibited with mercuric chloride, we show that AQP-1 is responsible for water transport across human VSMC membranes. Thus, this study provides evidence for a hitherto unrecognised role for aquaporins in mediating rapid water transport across human VSMC membranes. By analogy with other tissues, these data argue for an important role for AQP-1 in regulating transcellular fluid flow and tissue hydration.     

Temporary loss of perivascular aquaporin-4 in neocortex after transient middle cerebral artery occlusion in mice

The aquaporin-4 (AQP4) pool in the perivascular astrocyte membranes has been shown to be critically involved in the formation and dissolution of brain edema. Cerebral edema is a major cause of morbidity and mortality in stroke. It is therefore essential to know whether the perivascular pool of AQP4 is up- or down-regulated after an ischemic insult, because such changes would determine the time course of edema formation. Here we demonstrate by quantitative immunogold cytochemistry that the ischemic striatum and neocortex show distinct patterns of AQP4 expression in the reperfusion phase after 90 min of middle cerebral artery occlusion. The striatal core displays a loss of perivascular AQP4 at 24 hr of reperfusion with no sign of subsequent recovery. The most affected part of the cortex also exhibits loss of perivascular AQP4. This loss is of magnitude similar to that of the striatal core, but it shows a partial recovery toward 72 hr of reperfusion. By freeze fracture we show that the loss of perivascular AQP4 is associated with the disappearance of the square lattices of particles that normally are distinct features of the perivascular astrocyte membrane. The cortical border zone differs from the central part of the ischemic lesion by showing no loss of perivascular AQP4 at 24 hr of reperfusion but rather a slight increase. These data indicate that the size of the AQP4 pool that controls the exchange of fluid between brain and blood during edema formation and dissolution is subject to large and region-specific changes in the reperfusion phase.     

Neuromuscular adaptations to concurrent strength and endurance training

PURPOSE: The purpose of this study was to examine muscle morphological and neural activation adaptations resulting from the interaction between concurrent strength and endurance training. METHODS: Thirty sedentary healthy male subjects were randomly assigned to one of three training groups that performed 10 wk of 3-d x wk(-1) high-intensity strength training (S), cycle endurance training (E), or concurrent strength and endurance training (CC). Strength, quadriceps-muscle biopsies, computed tomography scans at mid-thigh, and surface electromyogram (EMG) assessments were made before and after training. RESULTS: S and CC groups demonstrated similar increases (P < 0.0001) in both thigh extensor (12 and 14%) and flexor/adductor (7 and 6%) muscle areas. Type II myofiber areas similarly increased (P < 0.002) in both S (24%) and CC (28%) groups, whereas the increase (P < 0.004) in Type I area with S training (19%) was also similar to the nonsignificant (P = 0.041) increase with CC training (13%). Significant increases (P < 0.005) in maximal isometric knee-extension torque were accompanied by nonsignificant (P 0.38) in the EMG/torque relation across 20 to 100% maximal voluntary contractions occurred in any group. A small 3% increase (P < 0.01) in thigh extensor area was the only change in any of the above variables with E training. CONCLUSIONS: Findings indicate 3-d x wk(-1) concurrent performance of both strength and endurance training does not impair adaptations in strength, muscle hypertrophy, and neural activation induced by strength training alone. Results provide a physiological basis to support several performance studies that consistently indicate 3-d x wk(-1) concurrent training does not impair strength development over the short term.     

Preferences in surgical waiting area amenities

The purpose of this needs assessment was to determine which waiting area amenities family members deem important to make them comfortable when waiting for news about surgical patients. A literature review was conducted, perioperative staff members were interviewed and surveyed, and family members were interviewed and surveyed. The findings indicate that family members have preferences for specific amenities. Items of highest importance include the service of a surgical nurse coordinator and a private room for consulting with physicians. Items of average importance include beepers and educational materials about the procedure. Items of least importance include a food cart and soft music. AORN J 75 (June 2002) 1077-1083.