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Biomedical subjects

M R Jackman

Publications and source records attributed to M R Jackman.

8 recordsLinked to original sources
PubMed1996

Characteristics of mitochondria isolated from type I and type IIb skeletal muscle.

Mitochondria isolated from rabbit soleus (98% type I) and gracilis (99% type IIb) skeletal muscle were compared for compositional differences. Whole muscle mitochondrial contents were 14.5 +/- 1.2 mg/g of wet weight in soleus and 5.3 +/- 0.6 mg/g in the gracilis muscle, a 2.7-fold difference. Maximal pyruvate plus malate oxidase activity in gracilis mitochondria was roughly 75% of that in soleus mitochondria. In contrast, glycerol 3-phosphate (G-3-P) oxidation was 10-fold greater in gracilis mitochondria. Both soleus and gracilis mitochondria exhibited additive pyruvate and G-3-P oxidase activities. In general, citric acid cycle enzyme activities were higher in soleus mitochondria. A notable exception was isocitrate dehydrogenase, which was twofold higher in gracilis mitochondria. Substrate cytochrome c reductase activities indicated that the electron transport chain (ETC) of soleus mitochondria possess roughly twice the capacity for both NADH and succinate oxidation. Similarly, the maximal activities of NADH dehydrogenase and succinate dehydrogenase were roughly twofold higher in soleus mitochondria. The findings demonstrate that mitochondria isolated from types I and IIb skeletal muscle differ substantially in composition. Furthermore, the relatively similar pyruvate plus malate oxidase activities in the face of markedly different ETC capacities suggest that the interaction between matrix dehydrogenases and the ETC may differ in mitochondria isolated from types I and IIb skeletal muscle.

Animals↗
PubMed1995

Effect of choline supplementation on fatigue in trained cyclists.

The availability of choline, the precurser of the neurotransmitter, acetylcholine, in the diet is sufficient to provide the body's requirements under normal conditions. However, preliminary evidence indicates that depletion of choline may limit performance, while oral supplementation may delay fatigue during prolonged efforts. A double-blind cross-over design was used to determine the relationship between plasma choline and fatigue during supramaximal brief and submaximal prolonged activities. Twenty male cyclists (ages 23-29) with maximal aerobic power (VO2max) between 58 and 81 ml.min-1.kg-1 were randomly divided into BRIEF (N = 10) and PROLONGED (N = 10) groups. One hour after drinking a beverage with or without choline bitartrate (2.43 g), cyclists began riding at a power output equivalent to approximately 150% (BRIEF) and 70% (PROLONGED) of VO2max at a cadence of 80-90 rpm. Time to exhaustion, indirect calorimetry and serum choline, lactate, and glucose were measured. Increases in choline levels of 37 and 52% were seen within one hour of ingestion for BRIEF and PROLONGED groups, respectively. Neither group depleted choline during exercise under the choline or placebo conditions. Fatigue times and work performed under either test condition for the BRIEF or PROLONGED groups were similar. Consequently, trained cyclists do not deplete choline during supramaximal brief or prolonged submaximal exercise, nor do they benefit from choline supplementation to delay fatigue under these conditions.

Administration, Oral↗
PubMed1994

Inhibition of apical but not basolateral endocytosis of ricin and folate in Caco-2 cells by cytochalasin D.

Apical and basolateral endocytic pathways in polarised Caco-2 cells were investigated by following the uptake, recycling and transcytosis of the galactose-binding protein toxin ricin, as a membrane marker. Differences in the extent and kinetics of lectin uptake, recycling and transcytosis were observed at the apical and basolateral domains and altered with the age of the cell monolayer. Treatment of polarised Caco-2 cells with cytochalasin D showed a domain-specific, concentration-dependent inhibition of apical endocytosis of ricin. Inhibition of apical endocytosis by cytochalasin D was not due to a gross change in brush border morphology, although actin stress fibres within the cell body were disrupted. It is not clear whether inhibition of apical endocytosis in polarized epithelial cells by cytochalasin D is caused simply by disruption of a mechanochemical motor involving microvillar actin filaments. The cytochalasin D effect was also observed when measuring uptake of folate, suggesting apical domain-specific inhibition of caveolar, as well as clathrin-mediated, endocytic routes.

Actin Cytoskeleton↗
PubMed1994

Mitochondrial function during heavy exercise.

Maximal rates, coupling, and control of oxidative phosphorylation were studied in isolated skeletal muscle mitochondria from rat and rabbit. Mitochondria were incubated under various conditions of temperature, pH, and substrate availability. A 20% decrease in coupling (ADP/O) was observed at 43 degrees C as compared to 37 degrees C in rat mixed skeletal muscle mitochondria. Changes in pH from 7.00 to 6.20 affected neither coupling nor maximal (state 3) respiration rates. Changing the substrate supply from pyruvate to palmitoyl-carnitine (+ malate) did not alter ADP/O, but markedly degraded the energy state sustained at submaximal ATP turnover. Thus, carbohydrate depletion may be associated with inhibition of contractile function and the recruitment of less economical higher threshold motor units. State 3 respiration of mitochondria from rabbit Type IIb fibers oxidizing pyruvate+malate+alpha-glycerophosphate was 27% higher than that of mitochondria from Type I rabbit skeletal muscle. However, the ADP/O ratio in the Type IIb preparation was 18% lower. The experimental findings suggest that temperature, substrate supply, and energetic differences between slow twitch and fast twitch motor units may impact the economy of mitochondrial oxygen utilization during heavy aerobic exercise, and thus contribute to the slow component of oxygen uptake.

Animals↗
PubMed1992

The post-synthetic sorting of endogenous membrane proteins examined by the simultaneous purification of apical and basolateral plasma membrane fractions from Caco-2 cells.

A subcellular fractionation method to isolate simultaneously apical and basolateral plasma membrane fractions from the human adenocarcinoma cell line Caco-2, grown on filter supports, is described. The method employs sucrose-density-gradient centrifugation and differential precipitation. The apical membrane fraction was enriched 14-fold in sucrase-isomaltase and 21-fold in 5'-nucleotidase compared with the homogenate. The basolateral membrane fraction was enriched 20-fold relative to the homogenate in K(+)-stimulated p-nitrophenylphosphatase. Alkaline phosphatase was enriched 15-fold in the apical membrane fraction and 3-fold in the basolateral membrane fraction. Analytical density-gradient centrifugation showed that this enzyme was a true constituent of both fractions, and experiments measuring alkaline phosphatase release following treatment with phosphatidylinositol-specific phospholipase C showed that in both membrane fractions the enzyme was glycosyl-phosphatidylinositol-linked. There was very little contamination of either membrane fraction by marker enzymes of the Golgi complex, mitochondria or lysosomes. Both membrane fractions were greater than 10-fold purified with respect to the endoplasmic reticulum marker enzyme alpha-glucosidase. Protein composition analysis of purified plasma membrane fractions together with domain-specific cell surface biotinylation experiments revealed the presence of both common and unique integral membrane proteins in each plasma membrane domain. The post-synthetic transport of endogenous integral plasma membrane proteins was examined using the devised subcellular fractionation procedure in conjunction with pulse-chase labelling experiments and immunoprecipitation. Five common integral membrane proteins immunoprecipitated by an antiserum raised against a detergent extract of the apical plasma membrane fraction were delivered with the same time course to each cell-surface domain.

Adenocarcinoma↗