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Biomedical subjects

G J Jones

Publications and source records attributed to G J Jones.

At least 55 records · Page 3Linked to original sources
PubMed1983

Microspectrophotometry of single rhabdoms in the retina of the honeybee drone (Apis mellifera male).

The relative absorption spectra of the bistable photopigment of single rhabdoms from the dorsal region of the retina of the honeybee drone were obtained using slices of retina fixed in glutaraldehyde; less accurate measurements on unfixed tissue gave difference spectra that were similar to those for fixed retinae. The method used was based on measurements of absorbance changes during saturating adaptations of the visual pigment to different monochromatic lights. It is similar to previous methods based on measurements of difference spectra amplitudes, but is simpler to use and more accurate. The predominant pigment has states that absorb maximally at 446 (rhodopsin) and 505 nm (metarhodopsin). In addition, there is a small amount of another pigment whose two states absorb maximally at approximately 340 (UV) and 460 nm.

Animals↗
PubMed1982

Effects of calcium and lanthanum on phosphate efflux from nonmyelinated nerve fibers.

Phosphate efflux was measured as the fractional rate of loss of radioactivity from rabbit vagus loaded with radiophosphate. The effects of changes in extracellular calcium and of lanthanum have been investigated. In Locke solution with normal, 0.9 mM, calcium and without phosphate, the fractional rate of loss was 1.62 X 10(-3) min-1 at 120 min after the beginning of the washing period and fell slowly (9% hr-1) during washing from 2 to 6 hr. Addition of calcium to the Locke solution produced a transient increase followed by a reversible maintained increase in phosphate efflux. The latter was 40 and 75% above efflux in normal calcium for 20 and 50 mM calcium, respectively. Removal of calcium, with or without addition of EGTA, produced only a transient increase in phosphate efflux, with no subsequent maintained change. Addition of low concentrations of lanthanum produced a reversible inhibition of phosphate efflux. Half-maximal inhibition was at 3.5 micro M lanthanum and appeared to be due to binding of lanthanum to more than one, probably two, sites. Measurements of inhibition by lanthanum at different calcium concentrations did not indicate any competition between calcium and lanthanum. It is suggested that a least a part of phosphate efflux depends on internal calcium and that lanthanum acts by preventing release of phosphate from the phosphate transport mechanism.

Animals↗
PubMed1982

Acetylcholine measured at short time intervals during transmission of nerve impulses in the electric organ of Torpedo.

1. The amounts of total acetylcholine (ACh) and ATP, and of vesicle-bound ACh were measured at short time intervals in the electrogenic tissue of Torpedo marmorata. The aim of this study is to approach with biochemical analysis the speed of electrophysiological phenomena.2. A stimulator coupled to a rapid freezer device was used to quench a number of tissue samples simultaneously, at different time intervals during transmission of a brief train of impulses at 100 Hz.3. The level of total ACh decreased significantly with the first ten impulses. Then a rapid but transient increase in total ACh occurred, reaching a maximum value by the fifteenth to sixteenth impulse.4. Vesicle-bound ACh did not exhibit any changes parallel to those of total ACh, and did not decrease beyond the control level during transmission of twenty impulses at 100 Hz.5. The amount of ATP in the tissue varied in close relation to that of total ACh. No significant phase shift was observed between the transmitter and the nucleotide and the ACh/ATP molar ratio was not significantly different from 1.6. The shortest time interval investigated in this work was 10 ms. The rate at which the pieces of tissue are quenched for biochemical measurements when plunged into a liquid at low temperature has been estimated. It has also been evaluated to what extent the freezing rate may distort measurements of the biochemical changes occurring in the tissue.7. It is concluded that fast freezing appears to be a valuable approach for investigating the rapid biochemical changes underlying cholinergic transmission; a better time resolution might be reached at the price, however, of greatly reducing the size of the samples. The second conclusion is that transmission of a brief train of impulses is accompanied by significant changes in the amount of extravesicular ACh.

Acetylcholine↗
PubMed1982

The inheritance of sinking-pre-beta lipoprotein and its relation to the Lp(a) antigen.

We have investigated the genetics of plasma sinking-pre-beta lipoprotein (sp beta) as determined by the method of Breckenridge and Maguire, using several approaches: (i) a population study, (ii) a twin study and (iii) the use of family data. In addition, by the use of split samples, the sp beta level as determined by us was correlated with Lp(a) typing carried out in Oslo by Dr. Kåre Berg. Although the sp beta level is a continuous character, the results clearly showed it to be to a considerable extent under the control of the major autosomal gene pair constituted by the alleles Lpa and Lp, which mainly control the production of the Lp(a) antigen, Lpa being dominant. In our data the boundary between the LpLp and LpaLp genotypes appeared to fall between the sp beta 2 and 3 mg% levels, while that between LpaLp and LpaLpa was in the 15 mg% region. These boundaries, which were inferred from both typing and population statistics, received good confirmation from the family data. It appears that some 88% of the variation in sp beta level is directly ascribed to segregation of Lpa and Lp. On the basis of the twin study and other data, we conclude that the residual observed variation in sp beta is almost entirely ascribed to analytical error of determination and polygenic effects, the influence of environment being negligible. The heritability is close to 100%.

Antigens↗
PubMed1981

Lipid class and molecular species interrelationships among plasma lipoproteins of normolipemic subjects.

As evidence of lipoprotein interconversion and/or equilibration, a gas-liquid chromatographic (GLC) examination was made of the lipid class and molecular species interrelationships among the major fasting plasma lipoprotein fractions within each of seven male and four female normolipemic subjects subsisting on free choice diets. The lipoprotein fractions were prepared by conventional ultracentrifugation and the lipid class and molecular species composition of the corresponding lipoprotein fractions were determined by GLC of the intact cholesterol and glycerol esters and of ceramides. In general, each lipoprotein fraction possessed a well defined lipid class composition, which was characterized by a dramatically decreasing triacylglycerol and an increasing phospholipid and cholesteryl ester content when progressing from the very low (VLDL), to the low (LDL2) and high (HDL) density lipoproteins, as already established by conventional analyses. However, the LDL2 contained about a two times higher proportion of total phospholipids as sphingomyelin than VLDL and HDL. Furthermore, the sphingomyelins of the HDL fraction contained about 30% more of the higher molecular weight species than the sphingomyelins of either VLDL or LDL. Smaller differences were seen in the molecular species composition of the phosphatidylcholines, cholesteryl esters and triacylglycerols among the corresponding fractions of lipoproteins. In general, the lipid class and molecular species distribution is incompatible with the hypothesis which postulates VLDL conversion into LDL and HDL under the influence of lipoprotein lipase and lecithin:cholesterol acyltransferase. The significant differences noted in the lipid class and molecular species distribution suggest that the true transformations of the lipoproteins are much more complex and may also involve cholesteryl ester-triacylglycerol, triacylglycerol and phosphatidylcholine exchanges via appropriate carrier plasma proteins, as well as possible phase separation of lipids during the removal of the excess surface material from the VLDL remnants, as already demonstrated in in vitro experiments. It is concluded that a direct GLC analysis of the neutral and polar lipid components of plasma lipoprotein classes provides important evidence of lipoprotein interrelationships which may be utilized to test existing and new hypotheses of lipoprotein interconversion.

Adult↗
PubMed1981

The correction factors for sucrose gap measurements and their practical applications.

The distribution of extracellular and intracellular potential in the sucrose gap apparatus, previously established for a single fiber using the cable equations for a core conductor model (Jirounek and Straub, Biophys. J., 11:1, 1971), is obtained for a multifiber preparation. The exact equation is derived relating the true membrane potential change to the measured potential differences across the sucrose gap, the junction potentials between sucrose and physiological solution, the membrane potential in the sucrose region, and the electrical parameters of the preparation in each region of the sucrose gap. The extracellular potential distribution has been measured using a modified sucrose gap apparatus for the frog sciatic nerve and the rabbit vagus nerve. The results indicate a hyperpolarization of the preparations in the sucrose region, of 60--75 mV. The hyperpolarization is independent of the presence of junction potentials. The calculation of the correction terms in the equation relating the actual to the measured potential change is illustrated for the case of complete depolarization by KC1 on one side of the sucrose gap. The correction terms in the equation are given for various experimental conditions, and a number of nomographic charts are presented, by means of which the correction factors can be rapidly evaluated.

Animals↗
PubMed1980

Comparative determination of plasma phospholipids by automated gas--liquid chromatographic and manual colorimetric phosphorus methods.

Plasma samples obtained during a prevalence study of hyperlipemia in a free-living urban population were analyzed for phosphatidylcholine, sphingomyelin and lysophosphatidylcholine content by automated high-temperature gas--liquid chromatographic (GLC) and manual colorimetric phosphorus (thin-layer chromatographic, TLC) methods. The GLC estimates were obtained from a quantitative analysis of the diacylglycerol, ceramide and monoacylglycerol moieties released from the parent phospholipids by digestion with phospholipase C, while the TLC estimates were derived by manual colorimetric phosphorus analyses of the individual phospholipid classes resolved by TLC. On samples analyzed over a two-year period the methods gave excellent correlation for the total phospholipids (r = 0.98), phosphatidylcholine (r = 0.98) and sphingomyelin (r = 0.90), but resulted in a poor agreement for lysophosphatidylcholine (r = 0.69). Comparable results were obtained for estimates of these phospholipids in plasma very low density, low density and high density lipoproteins. The between-method coefficient of variation ranged from 3 to 5% for phosphatidylcholine and from 5 to 10% for sphingomyelin. The relative error for the estimates of lysophosphatidylcholine ranged from 10 to 25%, and was due to the inclusion in the GLC estimates of a variable proportion of plasma free monoacylglycerols. Other differences between the two methods are due to various analytical errors and biases inherent in the two techniques. The within-day, within GLC, relative error averaged 1% for phosphatidylcholine, 3% for sphingomyelin and 5% for lysophosphatidylcholine. The apparent high precision and accuracy of the GLC method recommend it as an alternative to conventional direct methods of phospholipid analyses based on TLC isolation of lipid classes and colorimetric measurements of their phosphorus content. The GLC analyses of the plasma phospholipids are particularly convenient in conjunction with GLC measurements of plasma cholesterol and triacylglycerols, where a smaller throughput of samples is not a limitation and where both total amount and relative proportion of the lipids are of interest.

Autoanalysis↗
PubMed1980

Plasma lipoprotein levels and the prevalence of hyperlipoproteinemia in a Canadian working population.

The lipids and lipoproteins - cholesterol (C), triglyceride (TG) and high-density, low-density, very-low-density and sinking pre-beta-lipoprotein cholesterol (HDL-C, LDL-C, VLDL-C and SPB-C) - in plasma samples from 1620 fasting white adults and children from the Toronto-Hamilton area were analysed. The mean concentration of HDL-C was about 45 mg/dl in men and about 60 mg/dl in women, and the levels were constant throughout adult life in both sexes. Boys had higher mean HDL-C levels than men, but girls had lower mean HDL-C levels than women. Mean LDL-C levels, like total C levels, increased with age, from about 87 mg/dl in boys to 136 mg/dl in men, and from about 91 mg/dl in girls to 145 mg/dl in women. The mean levels of VLDL-C followed the TG patterns for age and sex, rising from about 7 mg/dl in boys to 26 mg/dl in men, and from about 11 mg/dl in girls to 19 mg/dl in women. SPB-C was detectable visually in 39% of the population and with the aid of densitometry in 54%; the levels were not related to age, sex or oral contraceptive use, and the median level was 3 mg/dl.Prevalence estimates of hyperlipoproteinemia showed that type IV was the most common, and it was found more than three times as often in men as in women. This was in part due to the customary use of plasma TG cut-off points that do not reflect the large difference in TG levels between males and females. Type IIA hyperlipoproteinemia was found in about 2% of the adults and type IIb in a further 1%. Types I, III and V were all rare. The prevalence of types II and IV hyperlipoproteinemia was four times greater in women using oral contraceptives than in nonusers in the same age range.

Adolescent↗
PubMed1978

Comparative determination of plasma cholesterol and triacylglycerol levels by automated gas--liquid chromatographic and autoanalyzer methods.

Plasma samples obtained during a prevalence study of hyperlipemia in a free living urban population were analyzed for total cholesterol and triacylglycerol content by automated high-temperature gas--liquid chromatographic (GLC) and automated colorimetric (Auto-Analyzer, AA11) methods. The analyses were done over a three-year period. The methods gave excellent overall correlation for both total cholesterol (r = 0.9811) and total triacylglycerols (r = 0.9739). Detailed comparisons of the results obtained by the two methods with natural samples over the entire concentration range, indicated that the GLC method gave cholesterol values 5--10 mg% lower and triacylglycerol values 10--20 mg% lower than the corresponding AA11 determinations. The differences between the two methods are attributed to an overestimation of the cholesterol and triacylglycerol levels by the AA11 method due to presence of variable amounts of interfering chromogens in the plasma extracts. The between-method relative error ranged from 3 to 5% for cholesterol and from 5 to 10% for triacylglycerols. The within-day standard deviation of GLC averaged 2.3 mg% for cholesterol and 3.5 mg% for triacylglycerols. The between-day standard deviation of the GLC method averaged about 6 mg% for both cholesterol and triacylglycerols. The within-day, within GLC, relative error averaged 1.12% for cholesterol and 2.66% for triacylglycerols. The apparent high precision and high accuracy of the GLC method recommend it as an alternative to the indirect methods of plasma cholesterol and triacylglycerol analysis, especially where a smaller throughput of samples is not a limitation and where both total amount and composition of the lipids is of interest.

Autoanalysis↗
PubMed1977

Normative standards of plasma cholesterol and triglyceride concentrations in Canadians of working age.

Fasting plasma cholesterol and triglyceride concentrations were determined for 6407 working Canadian adults aged 20 to 69 years in Toronto and Hamilton. Means, medians and 5th and 95th percentiles were ascertained from the data for men, women taking oral contraceptives or estrogen preparations, and women not taking such medication. Mean plasma cholesterol values (mg/dL) ranged in men from 168.3 at ages 20 to 24 years to 211.5 at ages 45 to 49 years, and in women using hormone preparations from 180.3 at ages 20 to 24 years to 224.2 at ages 50 to 54 years; corresponding values in women not using these preparations were 164.9 and 220.6. Plasma triglyceride means (mg/dL) ranged in men from 108.7 at ages 20 to 24 years to 166.7 at ages 40 to 44 years, in women using hormone preparations from 115.4 at ages 20 to 24 years to 145.3 at ages 45 to 59 years, and in women not using these preparations from 77.5 at ages 20 to 24 years to 112.4 at ages 50 to 54 years.

Adult↗
PubMed1976

Sodium-dependent influx of orthophosphate in mammalian non-myelinated nerve.

1. The rate of uptake of radiophosphate was measured in desheathed vagus nerves of rabbits mounted in an apparatus where the incubating solution flowed along the preparation. 2. Replacement of the Na of the Locke by either choline or Tris slowed the rate of uptake to about 10% of its value in Na; with K it was slowed to 20%; and with Li to 50%. 3. Measurements of the rate of uptake at different extracellular phosphate concentrations showed that in choline-Locke the influx of phosphate was proportional to the extracellular phosphate concentration, while in Locke the rate of inward flow showed a tendency to saturation with increasing phosphate concentrations. 4. Extracts of nerves after 45 min exposure to labelled solutions showed for different phosphate concentrations a slowing of the labelling of ATP, ADP and creatine-phosphate (CrP) and inorganic phosphate (Pi) when Locke was replaced by choline-Locke. 5. A similar slowing was found when, at 0-2 mM phosphate, the labelling of these compounds was measured at different times: application of choline-Locke reduced the rate of incorporation of 32P to about 15% of the rate in Locke. 6. In preparations that were loaded with radiophosphate and then washed with inactive solution, and the effluent fractionated, over 90% of the radioactivity was found in the inorganic phosphate fraction. 7. The efflux of 32P showed an initial exponential phase with a time constant of 20-30 min and a much slower one. The slow efflux had a rate constant of 0-0014 min-1 in 0-2 mM external phosphate. 8. Increasing the external phosphate concentration increased the efflux. 9. Prolonged incubation in choline-Locke reduced the efflux. 10. The influx of phosphate was calculated for different external phosphate concentrations using the rate of uptake of radiophosphate measured 45 min after the application of isotope and the corresponding efflux rate coefficient and the intracellular specific activities of the labelled compounds. 11. A correction was also introduced for diffusion, using the "limited biophase model". 12. The Na-sensitive influx, i.e. the difference between influx in Locke and influx in choline-Locke, showed saturation kinetics. 13. A Lineweaver-Burk plot for Na-sensitive uncorrected influxes gave a vmax of 16-7 mumole/kg wet wt. min and an apparent Km of 0-42 mM; for the corrected fluxes these values were 18-2 and 0-36. 14. It is concluded that a large part of phosphate influx and some of the phosphate efflux is mediated by a specific Na-dependent phosphate transport system. 15. This system seems to be present also in other types of nervous tissues and probably in many types of animal cells.

Adenosine Diphosphate↗