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Biomedical subjects

C M Jackson

Publications and source records attributed to C M Jackson.

At least 91 records · Page 5Linked to original sources
PubMed1979

Measurement of phospholipid monolayer surface potentials at a hydrocarbon-electrolyte interface.

The phospholipid monolayer spread at a hydrocarbon-electrolyte interface can be used as a model system for the plasma membrane and its properties and structure probed by measurements of surface pressure and surface potential. To facilitate such studies, (i) the theory of the vibrating plate (Kelvin) method of measuring surface potentials is reëxamined and a new interpretation given for the potentials measured and (ii) a new apparatus for performing these measurements is described. The theory and apparatus are illustrated by measurements on films of distearoyl phosphatidylcholine at the interface between 2,2,4-trimethylpentane (isooctane) and 0.1 M NaCl.

Cell Membrane↗
PubMed1979

Phospholipid monolayers at the hydrocarbon-electrolyte interface. The interrelation of film potential and film pressure.

Measurements of surface pressure of surface potential are reported for films of distearoyl phosphatidylcholine (density range: 0.15--2.65 . 10(18) molecules/m2) spread at the interface between 2,2,4-trimethylpentane and 100 mM NaCl. Low density behavior of the surface pressure is explained using classical viral theory. The behavior of the surface potential is qualitatively explained for all densities in terms of the dipole moments associated with the carboxyl groups and headgroups of the phosphatidylcholine.

Electrolytes↗
PubMed1978

Properties of the factor Xa binding site on human platelets.

The affinity (Ka) of human coagulation Factor Xa for thrombin-treated (to stimulate the release reaction) platelets has been determined to be 3 to 4 x 10(10) M-1 by equilibrium binding studies using 125I-labeled Xa. The binding of Factor Xa to platelets results in an increase of 300,000-fold in the apparent enzymatic activity of Xa in the conversion of prothrombin to thrombin. The activity of platelet surface Xa is approximately 15-fold greater than that observed with optimum concentrations of bovine Factor V and phospholipids in place of platelets. Ca2+ is required for the Xa-platelet interaction; the optimum concentration is 2.5 mM. Related coagulation factors, including Factor X, Factor IXa, diisopropylphosphoryl Factor Xa, and prothrombin do not complete with Factor Xa for the Xa binding sites. The rate of thrombim formation at saturating amounts of Xa is directly proportional to the number of platelets from 1 x 10(7) to 5 x 10(8) platelets/ml. Factor Xa bound to platelets is not inactivated by antithrombin III. An antibody that inhibits both human and bovine coagulation Factor V activity blocks both Xa binding to released platelets and the rapid thrombin formation associated with this binding, suggesting that Factor V from platelets is involved in the Xa-platelet interaction.

Binding Sites↗
PubMed1978

Comparison of methods for detecting specific IgM antibody in infants with congenital rubella.

Serum specimens from 14 infants with congenital rubella were examined for specific IgM antibody by six different methods. IgM-containing fractions were separated either by sucrose density-gradient centrifugation or by gel filtration through Sephadex G-200, and were then tested by the indirect immunofluorescence technique and by the haemagglutination-inhibition (HI) test (long-and short-incubation methods). Immunofluorescence staining of density-gradient fractions detected specific IgM in all 14 infants. The HI test (long method), applied to density-gradient fractions, was almost as sensitive, detecting antibody in 13 infants; the short method was less sensitive. The gel-filtration technique proved to be generally less satisfactory than sucrose density-gradient centrifugation. Evidence was obtained for the occurrence of as yet unclassified non-specific inhibitors in the serum of some infants. These inhibitors were deposited with the IgM on sucrose-density gradients and they could have been mistaken for rubella-specific IgM antibody, particularly in the HI test (long method).

Antibodies, Viral↗
PubMed1978

The mechanism of chlorothiazide-induced carbohydrate intolerance.

In order to establish the mechanism(s) of chlorothiazide-induced hyperglycemia, measurements of blood glucose, plasma insulin, liver glycogen and hepatic cyclic adenosine 3':5'-monophosphate (cyclic AMP) levels, and liver phosphodiesterase activity were made in rats administered 10, 25, 50 or 100 mg/kg of the drug. Comparison of data obtained on these animals with those from controls revealed significant and dose-dependent increases in blood glucose, decreases in liver glycogen, increases in hepatic cyclic AMP and inhibition of phosphodiesterase. Although basal insulin levels were significantly increased at the two higher doses of chlorothiazide, ratios of blood glucose/plasma insulin levels showed suppression of insulin secretion at all four doses. However, this suppression was not dose-related. All effects of the drug were maximal at 2 hours after subcutaneous administration. The results of this investigation indicate that the primary mechanism of chlorothiazide-induced carbohydrate intolerance is cyclic AMP-mediated stimulation of glycogenolysis and inhibition of glycogenesis. Suppression of insulin secretion is secondary but probably contributes to the hyperglycemia.

Animals↗
PubMed1977

Interaction of coagulation factor Xa with human platelets.

When human 125I-labeled Factor Xa is incubated with washed platelets, prothrombin, and Ca2+, a small amount of thrombin is formed which causes the platelet release reaction after a period of time that decreases as the Xa concentration is increased from 0.9 to 19 ng/ml. After a further lag period, the Xa binds reversibly to receptors on the platelet surface and rapid thrombin formation follows (3 units or 1 mug of thrombin formed per min per ng of Xa bound to 10(8) platelets). When platelets are treated with either htrombin (0.5 units/ml) or calcium ionophore A23187 prior to addition of Xa, binding begins immediately. Thrombin formation occurs at the platelet surface at rates that correlate with the amount of Xa bound. Dibutyryl cyclic AMP inhibits the release reaction, Xa binding, and rate of thrombin generation in parallel. The platelet Xa receptor is distinct from the previously described thrombin receptor and appears to be a protein because treatment of platelets with thrombin at 50 units/ml destroys Xa binding sites. The results suggest that specific receptors for Xa appear on the platelet surface after the release reaction occurs. The bound Xa catalyzes thrombin formation 1000-fold faster than does Xa added to reactions in which phospholipids are substituted for platelets.

Blood Platelets↗
PubMed1976

An inhibitory effect of salivary gland extirpation on the induction of mammary tumors in rats by N,N'-2,7-fluorenylenebisacetamide.

N,N'2-2,7-Flourenylenebisacetamide (2.7-FAA) was administered orally to 34 female, strain AXC/I rats. Nineteen were pretreated with the extirpation of the salivary glands. The remaining 15 rats received no surgical treatment. Six of these 15 unoperated rats developed mammary carcinomas and seven developed tumors at other sites, whereas none of 19 operated rats had mammary tumors but 8 rats had tumors at other sites. No tumor developed in 4 operated control rats that were on normal diet. The results demonstrate that pretreatment with extirpation of the salivary glands inhibited mammary tumor induction in rats by 2,7-FAA although it did not inhibit induction of other type tumors. The mechanism by which induction of mammary tumors was inhibited is not clear. Ovarian atrophy and hepatic necrosis were observed in both operated and unoperated rats ingesting 2,7-FAA but did not seem to affect carcinogenesis by the carcinogen. Lower body weight was observed in operated rats but it is not considered to be the major cause of a complete inhibition of mammary tumor induction.

2-Acetylaminofluorene↗
PubMed1975

The functional significance of vitamin K action. Difference in phospholipid binding between normal and abnormal prothrombin.

In comparison to normal prothrombin, the abnormal prothrombin produced in response to vitamin K antagonists has been found to bind much less tightly, if at all, to phospholipid surfaces. As a consequence, the activation of abnormal prothrombin by Factor Xa and Ca2+ is not accelerated by the addition of phospholipid to the mixture while the activation of normal prothrombin under these conditions is greatly accelerated by phospholipid addition. In the absence of phospholipid, however, the rate of activation of abnormal prothrombin by Factor Xa and Ca2+ in both the presence and absence of Factor Va is indistinguishable from that of normal prothrombin. The distribution of the partial proteolysis products during activation by Factors Xa, Va, and Ca2+ also appears to be the same for both prothrombins. These observations provide an explanation for the function in prothrombin activation of the gamma-carboxyglutamate residues formed in the vitamin K-dependent carboxylation of prothrombin.

Animals↗