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Biomedical subjects

J A Walker

Publications and source records attributed to J A Walker.

At least 127 records · Page 7Linked to original sources
PubMed1976

The probability of closure in aortocoronary vein bypass grafts.

A study of 540 patients who had the aortocoronary vein bypass operation (from several transplant teams) showed that grafts within a patient closed independently of one another during the first-two year postoperative period. For patients with a single vein graft, there was a 23% chance of closure during the first two year postoperative period. The chance that all grafts would close during this period for patients with two grafts was 5%, and it was 1% for patients with three grafts. The knowledge of these closure probabilities may be used by the surgeon when planning the optimal surgical maneuver.

Cardiac Catheterization↗
PubMed1976

Gunshot wounds of the ureter: a 15-year review of 63 consecutive cases.

We reviewed 63 consecutive cases of gunshot wounds of the ureter seen during a 15-year period. The importance of prompt recognition and aggressive surgical management is emphasized, with particular attention being placed on adequate debridement and spatulated splinted watertight ureteroureterostomy. Our philosophy of management for individual injuries is discussed along with our complications and results. This series is the largest reported to date of ureteral gunshot wounds.

Adolescent↗
PubMed1976

Genetic dissection of the photoreceptor system in the compound eye of Drosophila melanogaster.

Three mutations which eliminate specific types of photoreceptors in Drosophila were characterized. Of the eight photoreceptors in each facet, two mutations delete the outer six (R 1-6). The third eliminates R 7, one of the two central photoreceptors. Double mutants can be constructed in which only photoreceptor R 8 is present. The spectral sensitivities, photopigments, and behavioural properties of these mutants were investigated. R 1-6 have two sensitivity peaks, near 350 and 470 nm. These receptors contain a rhodopsin with these absorption peaks. It interconverts with a metarhodopsin that absorbs around 570 nm. R 7 is a U.V.-receptor, containing rhodopsin that absorbs around 370 nm and interconverts with a metarhodopsin which absorbs around 470 nm. R 8 is a non-adapting blue-receptor with a third type of rhodopsin. The properties of these photopigments explain the different sensitivities and spectral adaptation phenomena of the various photoreceptors. All the photoreceptors have input into phototaxis. Spectral analysis of this behaviour provides evidence for integration of the input from the different photoreceptors.

Animals↗
PubMed1976

Heart disease indicators in patients with aortocoronary bypass operation.

The incidence of cardiovascular disease risk factors and other indicators of cardiac impairment were studied in 478 patients prior to their aortocoronary vein bypass operation and 194 patients who had angiographic examination but did not undergo the operation because the clinical and coronary angiographic findings were not considered serious enough to warrant the bypass procedure. The patients referred for surgery had higher plasma cholesterol and triglyceride levels (259 and 219 vs 233 and 180 mg/100 ml), tended to be older (53 vs 49 years) and had more extensive occlusive disease (occlusion score 200 vs 70) than the group without the operation. There was little difference in the proportion of smokers (81 vs 83%) or prevalence of hypertension (33 vs 30%). In comparison with 9,964 participants of a local health screening program, both patient groups had markedly higher prevalence of smoking, hypertension, chest pain and previous myocardial infarcts.

Cholesterol↗
PubMed1975

Oyster-associated hepatitis. Failure of shellfish certification programs to prevent outbreaks.

During October and November 1973, outbreaks of hepatitis A associated with consumption of raw oysters occurred in Houston and in Calhoun, Ga. The oysters implicated in both outbreaks had been harvested in two Louisiana bays. Although the bays had been contaminated with polluted Mississippi River water two months before the oysters were harvested, at the time of harvesting the bays met national sanitation standards for shellfish growing and were certified for oyster fishing. These epidemics raise serious questions about the adequacy of shellfish sanitation monitoring systems currently in use.

Certification↗
PubMed1975

Polar head-group and acyl side-chain requirements for phospholipid-dependent (Na-+ plus K-+)-ATPase.

The abilities of different phospholipids to reactivate a lipid-depleted (Na-+ plus K-+)-ATPase (EC 3.6.1.3) have been compared. The phospholipids contained either the same group of hydrocarbon chains withhh different polar groups, or different hydrocarbon groups wit the same polar group; they were prepared by enzymic modification of the polar group of phosphatidylserine isolated from bovine brain and of phosphatidylcholine extracted from egg. Only the acidic phospholipids reactivated the ATPase but the amount of reactivation depended on the nature of the hydrocarbon chains as well as the polar group. These findings are discussed in relations to the compositions of the two different groups of fatty acyl chains constituting the hydrocarbon portions of the phospholipids.

Adenosine Triphosphatases↗
PubMed1975

Lipid requirement of the membrane sodium-plus-potassium ion-dependent adenosine triphosphatase system.

The dependence of the (Na-++K-+)-dependent ATPase (adenosine triphosphatase) (EC 3.6.1.3) on lipid has been examined in a number of different ways, with the use of various preparations from kidney tissue. The main findings were as follows. (1) The ATPase activities of the preparations examined were closely correlated with their total phospholipid content. (2) Extraction of the ATPase with deoxycholate or Lubrol W, combined with suitable salt-fractionation and washing procedures, removed phospholipid, cholesterol and enzymic activity in parallel; but activity was completely lost before all lipid had been removed. (3) The loss of activity could not be attributed to inhibition by residual detergent. (4) No selective removal of any particular phospholipid class by detergent could be detected. (5) Consistent reactivation of the Lubrol-extracted enzymes was obtained by adding dispersions of exogenous phospholipid, but only some, bearing a net negative charge, such as phosphatidylserine and phosphatidylglycerol, were effective. (6) The degree of reactivation was correlated with the amount of residual activity remaining after lipid depletion. (7) Partial purification of the ATPase, giving a 50-fold increase in specific activity, was not accompanied by selective enhancement of any particular class of phospholipid. We conclude that although the ATPase is dependent on phospholipid, only the reactivation results provide evidence for specificity.

Adenosine Triphosphatases↗
PubMed1975

Differential effects of lipid depletion on membrane sodium-plus-potassium ion-dependent adenosine triphosphatase and potassium ion-dependent phosphatase.

The phospholipid-dependence of the (Na-++K-+)-dependent ATPase (adenosine triphosphatase) (EC 3.6.1.3) and associated K-+-dependent phosphatase activity (EC 3.6.1.7) have been compared. Unlike the (Na-++K-+)-dependent ATPase activities, the K-+-dependent phosphatase activities of a number of different preparations were not closely correlated with their total phospholipid contents. After partial lipid depletion with a single extraction in Lubrol W the residual ATPase and phosphatase activities were correlated, but their magnitudes were quite different: on average only about 5% of the former remained compared with 50% of the latter. A similar differential effect on these activities was found after extraction with deoxycholate. In contrast with the ATPase, consistent restoration of the phosphatase activity of Lubrol-extracted enzymes by added exogenous phospholipids was not observed. We conclude that, although the K-+-dependent phosphatase may be lipid-dependent, the lipid requirement must be different from that of the complete ATPase system, and this difference should help investigations of their relationship.

Adenosine Triphosphatases↗