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Biomedical subjects

J D Robertson

Publications and source records attributed to J D Robertson.

At least 55 records · Page 3Linked to original sources
PubMed1989

Brain angiotensin II and baroreceptor reflex function in spontaneously hypertensive rats.

We examined whether the increase in baroreceptor reflex function previously reported in lifetime - captopril-treated spontaneously hypertensive rats (SHR) was due to an inhibition of brain angiotensin II mechanisms. Pregnant and lactating SHR were given oral captopril (100 mg/kg/day). After weaning, pups were maintained on captopril (50 mg/kg/day) until the study (19-21 weeks). Control rats received tap water. One week before study captopril-treated and control SHR were given an intracerebroventricular infusion of angiotensin II (7.5 ng/hr, osmotic pump) or vehicle (artificial cerebrospinal fluid). Baroreceptor reflex control of heart rate was assessed by the slope of the relation between the change in mean arterial pressure (mm Hg) versus the change in pulse interval (msec beat-1). Arterial pressure was raised or lowered by intravenous bolus injections of phenylephrine or nitroprusside, respectively. Central infusion of angiotensin II had no significant effect on mean arterial pressure in captopril or control SHR (captopril-angiotensin II 125 +/- 4 vs. captopril-vehicle 121 +/- 2; control-angiotensin II 169 +/- 5 vs. control-vehicle 173 +/- 7 mm Hg), but it produced a significant rise in basal heart rate (captopril-angiotensin II 371 +/- 10 vs. captopril-vehicle 323 +/- 8, p less than 0.0002; control-angiotensin II 338 +/- 7 vs. control-vehicle 312 +/- 8 beats/min, p less than 0.0183) and in daily water intake (captopril-angiotensin II 20.7 +/- 2.2 vs. captopril-vehicle 9.8 +/- 0.7, p less than 0.0426; control-angiotensin II 33.1 +/- 3.8 vs. control-vehicle 9.0 +/- 0.6 ml/100 g body wt, p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMed1989

Distribution of gap junctions and square array junctions in the mammalian lens.

The morphology of membrane specializations of the cortex and nucleus of bovine lenses has been analyzed for both isolated membrane fractions and intact tissue fragments. Fractions of fiber cell membranes isolated from the outer cortex and the inner nucleus of lenses have been compared using x-ray diffraction, electron microscopy, SDS polyacrylamide gels and Western blots. Each fraction has distinctive structural characteristics. In x-ray experiments, the cortical fraction gives no sharp equatorial reflections (from the plane of the membrane), whereas the nuclear fraction gives sharp equatorial reflections which index on a square lattice of 6.6 nm. In thin-section electron micrographs, the cortical fraction is composed primarily of closed vesicles and flat membrane sheets, some of which contain pentalamellar structures similar in appearance to the 16-18 nm thick gap junctions found in other tissues. The nuclear fraction contains mostly undulating membrane pairs which often show 11-14 nm pentalamellar profiles and occasionally thicker junctions. In freeze-fracture images the cortical membranes display irregular clusters of intramembrane particles which resemble gap junctions, whereas the nuclear membranes contain numerous large square arrays with a 6.6 nm repeat and few irregular clusters or individual intramembrane particles. Images of fragments of intact lenses used in the membrane isolations give similar results; in the cortex the area covered by gap junctions is over 50 times the area covered by square lattices, whereas nuclear fiber cell membranes contain large square arrays. Thus, cortical and nuclear fiber cell membranes have quite different morphologies. In particular, the size of the square arrays of protein increases as the fiber cells mature. SDS polyacrylamide gels from cortical and nuclear fractions are similar in that they both contain MP26 as the major band. However, Western blot analysis shows increasing quantities of lower molecular weight, 25 kD and 22 kD, cleavage products as one progresses from the cortex to the nucleus. These data indicate that MP26 and/or its cleavage products form square crystalline arrays in nuclear fibers. The morphology of these arrays suggests a role for MP26 in cell-to-cell adhesion.

Animals↗
PubMed1988

Changes in red cell density and related indices in response to distance running.

The red cell population in peripheral venous blood was characterised in 7 young males before and up to 16 days after a 21.1 km road race. There was a 1.9 +/- 2.4% (mean +/- SD) reduction in plasma volume immediately post race (p less than 0.05), an increase in serum osmolality from 277 +/- 4 mOsm.kg-1 to 291 +/- 14 mOsm.kg-1 (p less than 0.05) and a reduction in red cell water (64.4 +/- 0.3% to 63.4 +/- 0.4%, p less than 0.001). The latter was consistent with alterations in the manually derived MCV and MCHC values although the same Coulter derived values were unaltered. A concomitant increase in median red cell density in whole blood (1.1045 +/- 0.0009 g.ml-1 pre race to 1.1057 +/- 0.012 g.ml-1 immediate post race, p less than 0.05) was recorded by centrifugation through phthalate esters of different density. The changes in creatine content of the red cells suggested that during the race younger cells were released into the circulation but that 24 h to 72 h after the race the mean red cell age had increased. Similarly, fractionation of the red cells on discontinuous Percoll density gradients indicated that the cell population was significantly denser in all post race samples up to 72 h but had normalized by a 16 day sample; the osmotic fragility was similarly affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Fluid homoeostasis during prolonged low-intensity walking on consecutive days.

1. The effect on fluid homoeostasis of walking 37 km on each of 4 consecutive relatively cool days was studied in six male subjects. The daily exercise intensity was consistent and was equivalent to 17(1)% [mean (SE)] of maximum oxygen uptake for these subjects. 2. The diet during the study consisted of a mainly carbohydrate breakfast, consumed immediately before each day's exercise, and unrestricted access to a normal mixed diet after completion of each day's exercise. Water was allowed ad libitum during the walk. Food and fluid intake were recorded. 3. Body weight remained constant over the 4-day walk. The difference between total daily fluid intake and the corresponding 24 h urine output was 1684 (250) ml, 1621 (522) ml, 1107 (252) ml and 1406 (208) ml, respectively, on each of the 4 exercise days. 4. There was a calculated increase of 21.3(6.6)% in plasma volume over the 4-day walk; the largest daily change [11.3(2.9)%] occurred during the walk on day 1. The increase in plasma volume was maintained for at least 4 days after completion of the walk. 5. From day 2, serum sodium concentration tended to increase during the exercise period and fell to the pre-exercise concentration during the overnight rest periods. The concentration of the other measured serum constituents remained relatively constant, and serum osmolality did not alter over the study period.

Blood Proteins↗
PubMed1987

Faecal blood loss in response to exercise.

Recently qualitative tests have indicated that gastrointestinal bleeding during exercise may be an important contributory factor in sports anaemia. In six healthy men who walked 37 km on four consecutive days faecal haemoglobin content remained normal (reference range 0.10-2.53 mg/g faeces) with no significant differences between values. In 28 marathon runners who refrained from taking drugs or food containing blood the median faecal haemoglobin content increased by 0.42 mg/g faeces (95% confidence interval 0.12 to 0.83 mg/g) from 1.06 (0.86 to 1.31) mg/g before the race. In 13 runners who had taken drugs before the race the corresponding increase in the median faecal haemoglobin content was 0.87 (-0.03 to 2.20) mg/g from the value before the race of 0.93 (0.46 to 1.55) mg/g. Prolonged walking had no effect on gastrointestinal blood loss. Intense endurance exercise in the form of marathon running induced a significant but clinically unimportant increase. This may be exaggerated by the ingestion of drugs and assume importance in causing iron deficiency and sports anaemia. The use of drugs, particularly analgesics, by marathon runners should be actively discouraged.

Adult↗
PubMed1987

Influence of exercise on ascorbic acid status in man.

1. The response of circulating leucocytes with regard to changes in number, proportion of granulocytes and lymphocytes, as well as changes in the ascorbic acid (AA) concentration of plasma and isolated lymphocytes, were studied in nine men who ran a 21 km race. A marked leucocytosis was noted 5 min after the race, the predominant increase being in granulocytes (P less than 0.001) with smaller relative increases in circulating lymphocytes (P less than 0.01) and platelets (P less than 0.001). Numbers of leucocytes and platelets returned to pre-exercise levels within 24 h after the race. 2. The concentration of AA in plasma increased from 52.7 +/- 4.1 mumol/l before the race to 67.0 +/- 5.3 mumol/l within 5 min after the race (P less than 0.001). This increase in plasma AA concentration was positively correlated with the rise in plasma cortisol concentration during the race (r = 0.89; P less than 0.01). However, within 24 h after the race the plasma concentration of AA fell 20 +/- 4% below pre-exercise values (P less than 0.01) and remained low for at least the next 2 days (P less than 0.05). 3. Lymphocyte AA concentration increased from 15.6 +/- 0.6 to 19.7 +/- 0.9 mumol/g of lymphocyte protein during the race (P less than 0.01) but returned to normal levels within 2 days after the race. 4. It is suggested that the adrenal gland may be the major source of AA efflux into the circulation during exercise.

Adult↗
PubMed1987

Hematological changes associated with marathon running.

Coulter profiles with differential white cell counts, serum ferritin, and haptoglobin levels were determined in venous blood samples obtained from 90 males (M) and 25 females (F) immediately before and after completion of a competitive marathon (42.2 km) race. In an additional 20 male runners, the same measurements were performed serially during the 24 h following their completion of the race. In the pre-race samples from 90 M and 25 F, hypoferritinemia was present in 4/22 M and 1 F found to be mildly anemic. Neutropenia was detected in 4 M and 3 F and mild thrombocytopenia in 2 M. Haptoglobin levels were normal in all the female runners but reduced (less than 0.3 g/l) in 6 M. All post-race samples (88 M and 25 F) were characterized by a reactive neutrophilia and thrombocytosis including those with pre-race neutropenia or thrombocytopenia. An unexpected and incompletely explained sex difference in packed cell volume (PCV) response was observed. In males, the mean PCV increased from 0.425 +/- 0.021 to 0.444 +/- 0.028 (P less than 0.0001) whereas in females it decreased from 0.437 +/- 0.029 to 0.423 +/- 0.036 (P less than 0.05). In the post-race samples, anhaptoglobinemia was found in 13/88 M and 4/25 F. In the 20 male runners studied serially for 24 h after the race, the major changes involved a progressive increase in mean plasma volume (17.4% +/- 12.2% at 24 h) compared with the pre-race value, a progressive and significant increase in MCH and MCHC probably indicating a loss in red cell water and the gradual reversion of the reactive neutrophilia and thrombocytosis to basal levels.

Adult↗
PubMed1986

The osmotic concentration of parietal muscle of the hagfish Myxine glutinosa L., including estimates of free and bound constituents.

The principal osmotic constituents of plasma and of muscle before and after ultracentrifugation have been determined. By analysing the muscle fluid and centrifuged muscle and determining their extracellular fluid (inulin space), ion-binding in the cells was estimated at Na 26%, K 0.3%, Ca 93%, Mg 24%, Cl 21% and P 10%. Muscle fluid was 4.9% (2.7-7.4%) hyperosmotic to plasma. This is discussed in relation to calculated osmolality of muscle and plasma.

Animals↗
PubMed1986

Particles and pits matched in native membranes.

We have obtained high resolution electron microscopic images of complementary membrane surface replicas of purified microsomal vesicles from pig kidney outer medulla containing Na+,K+-ATPase. Ultra-rapid freezing of a membrane suspension was followed by fracturing and replicating of the liquid helium cooled specimen under ultra-high vacuum conditions free of hydrocarbon contaminants. The protoplasmic fracture faces are populated with intramembrane particles while the external fracture faces reveal complementary pits. This is the first demonstration of extended precise matching of individual intramembrane particles and their corresponding pits in biological membranes containing transmembrane proteins. The data are also consistent with the theory that the majority of Na+,K+-ATPase mass is located at the protoplasmic half of the membrane.

Animals↗
PubMed1986

Haematological changes due to triathlon competition.

A twelve parameter blood cell profile has been measured in 6 subjects before and after each phase of triathlon event. This involved 29 miles cycling, 12 miles running and finally 18.5 miles canoeing. There was a significant decrease in plasma volume (8.7% +/- 3.1%, p less than 0.001) following the first phase (cycling); this decrease was sustained to the end of the event. A substantial increase in the number of circulating leukocytes after cycling (84 +/- 58%) and running (255 +/- 83% of pre-event value) was observed. There was no further leucocyte increment after the canoeing stage which may indicate that the circulating concentration of these cells was maximal after running. Fluid shifts following the postural alteration accompanying the different types of exercise and subject variability may have masked any subtle changes in the red cell parameters.

Adult↗
PubMed1985

Membrane specializations in mammalian lens fiber cells: distribution of square arrays.

Fragments of intact rat, pig and bovine lenses and isolated membranes from bovine lenses were examined by freeze-fracture-etch electron microscopy employing samples ultra-rapidly frozen in the absence of fixatives or cryoprotectants. Complementary replicas of the bovine outer cortex clearly display small patches of square arrays (6.6 nm repeat) as structures distinct from gap junctions in the same membranes. In the outer cortex square arrays appear in single membranes where the extracellular space is not thinned, whereas gap junctions, as in other tissues, only occur where the extracellular space is greatly attenuated. Square arrays in the middle cortex appear as patches of varying size surrounded by smooth membrane fracture faces. Within the undulating membranes of tongue-and-groove interdigitations in the inner cortex and nucleus, the square arrays are extensive and are located specifically on the regions which have convex curvature toward the cytoplasm. Square crystalline regions alternate with non-crystalline regions within each membrane of an undulating pair. Across the extracellular space, crystalline regions are matched with non-crystalline regions, thus making it unlikely that the square array participates in intercellular communication. Because the undulations occur in isolated membranes following urea washing to remove cytoplasmic and extrinsic membrane proteins, the square arrays probably play a crucial role in the formation of the undulations and in the maintenance of membrane curvature. X-ray diffraction experiments show reflections from the crystalline square array for all twenty of our preparations of isolated membranes. These x-ray experiments indicate that the square arrays observed by freeze-fracture are abundant in lens fiber cell membranes.

Animals↗
PubMed1984

Characterization of (Na+ + K+)-ATPase liposomes. I. Effect of enzyme concentration and modification on liposome size, intramembrane particle formation and Na+,K+-transport.

Rabbit renal (Na+ + K+)-ATPase (EC 3.6.1.3) was purified and incorporated into phosphatidylcholine liposomes. Freeze-fracture analysis of the reconstituted system reveals intramembrane particles formed by (Na+ + K+)-ATPase molecules which are randomly distributed on concave and convex fracture faces. The reconstituted (Na+ + K+)-ATPase performs active Na+,K+-transport. The distribution of particles as well as the rate of active transport are directly proportional to the (Na+ + K+)-ATPase protein concentration used for reconstitution, while the total amount of sodium and potassium ions exchanged by ATP per volume vesicle suspension reaches maximum when each vesicle contains on the average more than two particles. (Na+ + K+)-ATPase pretreated with ouabain or vanadate yields the same particle density and vesicle size as control enzyme. However, detergent-denatured enzyme loses its ability to form intramembrane particles or to increase the vesicle size indicating that the lipids surrounding the protein part of the molecule are essential for the reconstitution process. The vesicle diameter increases as a function of the number of particles per vesicle. Histograms of the size distribution become wider with increasing intramembrane particle density and tend to show more than one maximum.

Animals↗
PubMed1984

Characterization of (Na+ + K+)-ATPase liposomes. II. Effect of alpha-subunit digestion on intramembrane particle formation and Na+,K+-transport.

The effect of the protein structure of (Na+ + K+)-ATPase on its incorporation into liposome membranes was investigated as follows: the catalytic alpha-subunit of (Na+ + K+)-ATPase was split into low-molecular weight fragments by trypsin treatment and the digested enzyme was reconstituted at the same protein concentration as intact control enzyme. The reconstitution process was quantified by the average number of intramembrane particles appearing on concave and convex fracture faces after freeze-fracture of the (Na+ + K+)-ATPase liposomes. The number of intramembrane particles as well as their distribution on concave and convex fracture faces is not modified by the proteolysis. In contrast, the ATPase activity and the transport capacity of the (Na+ + K+)-ATPase decrease progressively with increasing incubation times in the presence of trypsin and are abolished when the original 100 000 molecular weight alpha-subunit is no longer visible by sodium dodecylsulfate gel electrophoresis. Apparently, functional (Na+ + K+)-ATPase with intact protein structure and digested, non functional enzyme consisting of fragments of the alpha-subunit reconstitute in the same manner and to the same extent as judged by freeze-fracture analysis. We conclude that, while trypsin treatment modifies the (Na+ + K+)-ATPase molecule in a functional sense, it appears not to modify its interaction with the bilayer in producing intramembrane particles. On the basis of our results, we propose a lipid-lipid interaction mechanism for reconstitution of (Na+ + K+)-ATPase.

Animals↗
PubMed1984

Analysis of the three-dimensional structure of the urinary bladder epithelial cell membranes.

The three-dimensional structure of the luminal membrane of the mammalian urinary bladder has been determined using electron micrographs of tilted membranes preserved in neutralized potassium phosphotungstate stain. The density map consists of 12 stain-excluding regions, 57 A thick, that are organized as an inner ring of 6 and an outer ring of 6, plus a small stain-excluding feature directly on the sixfold axis. Only the luminal surface of the membrane can be observed suggesting that at the resolution of the reconstruction the cytoplasmic surface is smooth.

Animals↗
PubMed1983

The chromaffin granule as a model for membrane fusion: implications for exocytosis.

Rapid freeze/freeze-fracture and thin section electron micrographic studies of the Ca2+-promoted aggregation and fusion of isolated bovine adrenal medullary chromaffin granule membranes show that the granules undergo a series of morphological changes. The contact region becomes quite extensive and the membrane curvature changes radically at the edge of the contact site. The core material retracts away from the contact site leaving an electron lucent "stripe"; however, it remains adjacent to the membrane in the non-contact areas. The pentalaminar double membrane of the contact region often shows breaks. Close examination reveals that the two granule membranes have fused and become one continuous membrane. Rearrangement of large membrane associated particles (MAPs) can be seen by freeze fracture after Ca2+-promoted granule-granule contact. The broken pentalaminar septum becomes smaller and may break down into globular structures. These observations suggest a series of reactions in which the granules first form an encounter complex, then a stable complex. The membranes within the contact region undergo lateral displacement of the proteins and phase separations of the lipids, and then fuse. Analysis of the kinetics of turbidity and fluorescence changes during granule aggregation and fusion support the main postulates of the model. The initial events of aggregation are facilitated by putative recognition proteins and K+ will promote all activities except fusion. Recent observations that several soluble proteins (synexin, and albumin) will act as fusogens are discussed in terms of the relevance to exocytosis in vivo.

Animals↗
PubMed1982

The structure of junctions between lens fiber cells.

Junctions which have been isolated from bovine lens may correspond to the tongue-and groove interdigitations observed between intact cells. These junctions have an overall thickness of 13-14 nm, a striking undulating surface topology, and contain protein subunits of congruent to 27 000 daltons which are arranged in a 6.6-6.7-nm square lattice in the plane of each membrane. A similar square-lattice structure has been observed in junctions from fragments of intact rate lens. Junctions from both sources are structurally different from "typical' gap junctions.

Animals↗