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J McMillin-Wood

Publications and source records attributed to J McMillin-Wood.

9 recordsLinked to original sources
PubMed1983

Sodium-calcium exchange in dog heart mitochondria: effects of ischemia and verapamil.

Na+ - Ca2+ exchange was studied in two preparations of dog heart mitochondria isolated from normal and ischemic muscle following occlusion of the circumflex (CFX) coronary artery with or without prior verapamil infusion. Na+ - Ca2+ exchange in mitochondria isolated using polytron homogenization showed sigmoidal kinetics with phosphate, whereas mitochondria isolated using gentle nagarse treatment showed hyperbolic kinetics and a Vmax 60% greater than the polytron preparation. Nagarse did not alter the sigmoidal kinetics or exchange velocities of the polytron mitochondria observed with phosphate. With acetate, both preparations exhibited hyperbolic kinetics, and the sodium required for half-maximum activity was increased. Verapamil inhibited Na+ - Ca2+ exchange in both preparations with phosphate, but not with acetate. Thirty or sixty minutes of acute ischemia following CFX occlusion produced significant epicardial surface S-T elevation in the ischemic area and a decrease in myocardial segment shortening. Na+ - Ca2+ exchange of both ischemic preparations was depressed, and the kinetics of the polytron preparation changed to hyperbolic. Pretreatment of the experimental animals with verapamil (0.3 mg/kg) before 60 min of ischemia protected the exchange rates in both preparations, and the sigmoidicity of the polytron mitochondria was retained.

Animals↗
PubMed1982

Exercise-induced alterations of hepatic mitochondrial function.

In order to examine the effect of a single bout of exercise on hepatic mitochondrial function, starved untrained male rats swam at 34-35 degrees C with a tail weight (5% of body wt.) for 100 min. The rates of ADP-stimulated and uncoupled respiration were higher in the mitochondria isolated from the exercised rats regardless of the substrate utilized. Succinate-linked Ca2+ uptake was 48% greater in the exercised group; however, Ca2+ efflux was markedly depressed. The inhibition of Ca2+ uptake by Mg2+ was higher in the control group, so that the difference in Ca2+ uptake between the two groups was greater in the presence of Mg2+ than in its absence. The response of phosphorylating respiration and Ca2+ fluxes to exogenous phosphate and the pH of the assay medium differed in the exercise group. These observations with the exercised group were not related to non-specific stress. The exercise-induced mitochondrial-functional alterations are reminiscent of those obtained from mitochondria isolated from glucagon- or catecholamine-treated sedentary rats. Thus, adrenergic stimulation as well as other factors may be operating during exercise, leading to an alteration of mitochondrial function in vitro.

Animals↗
PubMed1981

Evidence for a calcium-sensitive factor which alters the alkaline pH sensitivity of sarcoplasmic reticulum calcium transport.

Oxalase-supported, ATP-dependent Ca2+ uptake by cardiac and skeletal muscle sarcoplasmic reticulum (SR) exhibits a pH profile with the maximal rate of Ca2+ uptake at pH 6.6-6.8 and marked inhibition (90-95%) at pH 7.4-7.6, a point at which Ca2+-dependent ATPase activity is optimal. These observations are noted when the SR is first preincubated in media containing no added Ca2+. This alkaline pH inhibition is not caused by an irreversible perturbation since the Ca2+ uptake rate is fully restored by changing the alkaline pH preincubation medium to pH 6.8. When SR is preincubated with added Ca2+, Ca2+ uptake at alkaline pH (7.4-7.6) is only inhibited by 10-30%. Ca2+ uptake at pH 6.8 is the same regardless of preincubation conditions. A depressed oxalate permeability is not a factor in the observed alkaline pH inhibition of Ca2+ uptake. At alkaline pH, the relationship between the preincubation Ca2+ concentration and the rate of Ca2+ uptake is hyperbolic; the half-maximal free Ca2+ concentration for stabilization of Ca2+ uptake is 8-15 microM with a Vmax equal to the velocity at the optimal pH. The Hill coefficient is 1.0, implying a single class of Ca2+-requiring sites for stabilization at alkaline pH. In contrast to its effect on Ca2+ uptake, the presence of Ca2+ during preincubation does not alter the pH sensitivity of Ca2+-dependent ATPase activity. Thus, the presence of Ca2+ during preincubation may stabilize a state of the CaATPase, conducive to the coupling of net Ca2+ translocation to Ca2+-dependent ATPase activity, which is ordinarily opposed by alkaline pH. The data suggest a single class of Ca2+-requiring sites which favors this coupled state.

Animals↗
PubMed1980

Dissociation between mitochondria calcium ion release and pyridine nucleotide oxidation.

In the presence of phosphate, both acetoacetate and palmitoyl-coenzyme A induce pyridine nucleotide oxidation, swelling of mitochondria, and Ca2+ release. However, when mitochondria accumulate Ca2+ in the presence of lactate, neither acetoacetate nor palmitoyl-CoA addition results in Ca2+ release and no swelling is observed. If ruthenium red is added prior to these releasing agents, a 10-fold greater rate of Ca2+ efflux is observed when phosphate is present compared to lactate alone. Although acetoacetate produces significant oxidation of NADH in the lactate-supplemented medium, no Ca2+ release occurs. In the lactate medium, no oxidation of pyridine nucleotide was seen following palmitoyl-CoA addition. Lactate-supported Ca2+ accumulation (+/- N-ethylmaleimide) produces a transient respiratory stimulation associated with active Ca2+ uptake. Addition of phosphate to Ca2+-loaded mitochondria (lactate medium) promotes respiratory stimulation and Ca2+ efflux upon addition of acetoacetate or palmitoyl-CoA. When N-ethylmaleimide is present to inhibit the phosphate-hydroxyl exchange, no efflux of Ca2+ occurs after addition of phosphate and acetoacetate or phosphate and palmitoyl-CoA. The ionophore, A23187, produces Ca2+ release from mitochondria in either lactate (+/- N-ethylmaleimide) or phosphate medium. These results suggest that activation by the reduction state of mitochondrial pyridine nucleotides but may also depend upon the nature of the accompanying anion, as well as membrane permeability alterations.

Acetoacetates↗
PubMed1980

Calcium uptake by two preparations of mitochondria from heart.

Ca/+ transport and respiratory characteristics of two preparations of cardiac mitochondria (Palmer, J.W., Tandler, B. and Hoppel, C.L. (1977) J. Biol. Chem. 252, 8731-8739) isolated using polytron homogenization (subsarcolemmal mitochondria) and limited Nagarse exposure (intermyofibrillar mitochondria) are described. The Nagarse procedure yields mitochondria with 50% higher rates of oxidative phosphorylation than the polytron-prepared mitochondria in both rat and dog. Rat hear intermyofibrillar mitochondria contain 50% more cytochrome aa3 than the polytron preparation, whereas in the dog, cytochrome aa3 content is not significantly different. Cytochrome oxidase activities and cytochrome c, c1 and b contents were comparable in both populations of rat and dog heart mitochondria. The V of succinate-supported Ca2+ accumulation for Nagarse-prepared mitochondria from rat heart was 1.8-fold higher than the polytron-prepared mitochondria. In dog heart, the Nagarse preparation showed a 3.0-fold higher V for Ca2+ uptake compared to the polytron preparation. A lower apparent affinity for Ca2+ was demonstrated in the intermyofibrillar mitochondria for both species (Km is 2-2.5-fold higher). The Hill coefficient was 1 both mitochondrial types. Subsarcolemmal mitochondria from both species were treated with Nagarse to determine the role of this treatment on the observed differences. Nagarse did not alter any kinetic parameter of Ca2+ uptake. The properties of these mitochondria with reference to their presumed intracellular location may pertain to the role of mitochondria as an intracellular Ca2+ buffering mechanism in contractile tissue.

Absorption↗
PubMed1980

Mitochondrial water in myocardial ischemia: investigation with nuclear magnetic resonance.

Nuclear magnetic resonance studies of mitochondria isolated from ischemic hearts after coronary vessel occlusion indicated a decrease in water proton relaxation times. This change coincided with a decrease in the hydration of the samples. It is suggested that in ischemia, changes in macromolecular hydration may be one of the first mechanisms to alter function in the mitochondria, which are vital to the energy-transducing process in heart muscle.

Animals↗
PubMed1980

Respiration-dependent calcium ion uptake by two preparations of cardiac mitochondria. Effects of palmitoyl-coenzyme A and palmitoylcarnitine on calcium ion cycling and nicotinamide nucleotide reduction state.

Ca(2+) uptake and the effect of the uptake inhibitors palmitoyl-CoA and palmitoylcarnitine were examined in two preparations of dog cardiac mitochondria. Mitochondria prepared by using the Nagarse technique was 2.5-fold more active in respiration-dependent Ca(2+) uptake than were mitochondria isolated by using the Polytron procedure. Palmitoyl-CoA and palmitoylcarnitine inhibited Ca(2+) uptake in both preparations uncompetitively, with K(i,app) 0.4 and 20mum. Ca(2+)-uptake rates were related to, or influenced by, the concentration of mitochondrial reduced nicotinamide nucleotides, with uptake slowing as this concentration decreased. When most of the nicotinamide nucleotides was oxidized, Ca(2+) release and respiratory stimulation were observed. In the presence of Ruthenium Red and palmitoyl-CoA, oxidation of nicotinamide nucleotides was abolished and the time to Ca(2+) release was shortened corresponding to the time of onset of nicotinamide nucleotide oxidation in the absence of Ruthenium Red. The results suggest that NAD(P)H oxidation in the presence of rotenone was a consequence of Ca(2+) re-uptake and that net Ca(2+) release could be observed as reduced nicotinamide nucleotide concentrations declined. Although nicotinamide nucleotide oxidation occurred in the presence of rotenone, it was not linked in an apparent manner to acyl-group metabolism (palmitoylcarnitine was less effective than palmitoyl-CoA). Therefore either a by-pass of the rotenone block or a direct interaction of NAD(P)H with the Ca(2+)-uptake process was possible. Loss of NADH occurred before respiratory stimulation, and this loss may relate to decreased coupling efficiency at sites 2 and 3 of the respiratory chain, as suggested by others [Bhuvaneswaran & Wadkins (1978) Biochem. Biophys. Res. Commun.82, 648-654].

Acyl Coenzyme A↗
PubMed1980

Populations of rat skeletal muscle mitochondria after exercise and immobilization.

We slightly modified an existing procedure (Palmer et al., J. Biol. Chem. 252: 8731-8739, 1977) to isolate two distinct populations of mitochondria from rat skeletal muscle; initial brief Polytron homogenization released the subsarcolemmal mitochondria, and brief exposure of the resultant intact myofibrils to the proteolytic enzyme, Nagarse, extracted the intermyofibrillar mitochondria. The intermyofibrillar mitochondria differed from the subsarcolemmal mitochondr. ia by higher state III respiration measurements and enzymatic activities. These two populations of mitochondria were then isolated from the gastrocnemius muscle that had been induced to perform different amounts of contractile activity. The endurance training program of daily running significantly increased state III respiration and respiratory control index in the subsarcolemmal mitochondria, but the program did not increase these measurements in the intermyofibrillar mitochondria. In addition, 2 days of hindlimb immobilization resulted in a significant decrease in state II respiration and the respiratory control index of the subsarcolemmal mitochondria; however, immobilization did not affect the intermyofibrillar mitochondria. These measurements suggest that the subsarcolemmal mitochondria adapt in response to chronic changes in the level of contractile activity.

Adaptation, Physiological↗