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T M Nosek

Publications and source records attributed to T M Nosek.

At least 37 records · Page 2Linked to original sources
PubMed1996

Hydrogen peroxide disrupts Ca2+ release from the sarcoplasmic reticulum of rat skeletal muscle fibers.

Reactive oxygen species such as superoxide (O2-) and H2O2 are produced at low levels in resting muscles and at substantially higher levels in exercising muscles. Increased respiratory activity with exercise leads to O2- production by the NADPH oxidase reaction and the subsequent generation of H2O2 from O2- by spontaneous dismutation or by the superoxide dismutase reaction. The long-lasting (24-h) depression of contractile function after exercise has been linked to damage of one or more proteins important in the excitation-contraction coupling process. We studied mechanically and chemically skinned fibers from the extensor digitorum longus muscle of the rat to evaluate the effects of a 5-min exposure to 1.0 mM H2O2 on muscle function. We found that H2O2 had no effect on the isometric force-producing properties of the contractile apparatus or on Ca2+ uptake by the sarcoplasmic reticulum. It did, however, significantly affect Ca2+ release from the sarcoplasmic reticulum. Maximum depolarization-induced Ca2+ release was inhibited, and the sensitivity to depolarization was decreased. Ca(2+)-induced release was completely blocked. We conclude that elevated levels of H2O2 with exercise are capable of damaging one or more proteins of the excitation-contraction coupling process to produce a disruption in function that can account, at least in part, for the long-lasting effects of fatiguing stimulation.

Animals↗
PubMed1995

The effect of 2,3-butanedione 2-monoxime (BDM) on ventricular trabeculae from the avian heart.

2,3-butanedione 2-monoxime (BDM, 3-30 mM) decreased twitch force of intact ventricular trabeculae isolated from 19-day embryonic chick hearts in a dose-dependent manner. The responses to BDM were rapid and reversible. In an attempt to determine the cellular basis for the inhibitory effect of BDM, experiments were carried out on skinned muscle fibres and isolated myocytes. In trabeculae skinned with Triton X-100, BDM depressed maximum calcium activated force (Fmax) with an IC50 of 14 mM. At 3 mM BDM, the proportional decrease in twitch force in intact tissue was similar to that of Fmax in skinned tissue. At higher BDM concentrations (10 and 30 mM), however, the proportional decrease in twitch force was greater than that of Fmax. BDM (up to 10 mM) had no effect on the normalized force-pCa relationship. In saponin-skinned preparations, BDM (3 and 30 mM) released calcium from the fully loaded sarcoplasmic reticulum to a slightly greater extent in the absence of calcium (pCa 8.5) than in the presence of a fixed level of free calcium (pCa 5.5). Whole cell patch clamping of freshly isolated chick myocytes demonstrated that BDM caused a dose-dependent decrease in the T- and L-type calcium current. Therefore, at low BDM concentrations (3 mM), the decrease in twitch force can be ascribed predominantly to depression of the contractile apparatus while, at higher concentrations of BDM, there is an additional inhibitory effect of BDM on excitation-contraction coupling.

Animals↗
PubMed1994

Fatigue of rapid and slow onset in isolated perfused rat and mouse diaphragms.

Muscle fatigue was studied in the isolated perfused rat (66% oxidative fibers) and mouse (99% oxidative fibers) diaphragms. Both muscles displayed two fatigue patterns when exposed to 333-ms trains of 20-Hz stimulation. A rapid fatigue pattern appeared within each contractile train as an immediate progressive twitch-by-twitch diminution in contractility [a decrease in maximal isometric twitch tension (T) and maximal rate of T development]. An intertrain slow fatigue pattern also appeared as a progressive train-by-train diminution in contractility and an increased maximal rate of relaxation normalized to T. A reduction in the stimulatory frequency from 20 to 2 Hz caused a considerable diminution in the rapid fatigue pattern. These data suggest that rapid fatigue results from the time course of mechanical restitution, the time necessary for the Ca2+ channels of the sarcoplasmic reticulum to recover from inactivation. The slow fatigue pattern, on the other hand, is thought to be due to changes in the intracellular milieu. The difference in sensitivity of the rat and mouse diaphragms to rapid and slow fatigue is apparently related to differences in their fiber type composition. Thus, as would be expected, the mouse diaphragm, composed of only oxidative fibers, is less susceptible to slow fatigue compared with the rat diaphragm. On the other hand, it is more susceptible to rapid fatigue.

Animals↗
PubMed1993

Influence of ionic strength on contractile force and energy consumption of skinned fibers from mammalian and crustacean striated muscle.

Increased ionic strength decreases maximal calcium-activated force (Fmax) of skinned muscle fibers via mechanisms that are incompletely understood. In detergent-skinned fibers from either rabbit (psoas) or lobster (leg or abdomen), Fmax in KCl-containing solutions was less than in potassium methanesulfonate (KMeSO3), which we showed previously was the least deleterious salt for adjusting ionic strength. In either salt, lobster fibers were considerably less sensitive to elevated ionic strength than rabbit fibers. Trimethylamine N-oxide (TMAO, a zwitterionic osmolyte found in high concentration in cells of salt-tolerant animals) increased Fmax, especially in high KCl solutions. In this regard, TMAO was more effective than a variety of other natural or synthetic zwitterions. In rabbit fibers, increasing ionic strength decreases Fmax but has little effect on contractile ATPase rate measured simultaneously using a linked-enzyme assay. Thus high salt increases the tension-cost of contraction (i.e. ratio ATPase/Fmax). At both high and low salt, TMAO decreases tension-cost. Given a simple two-state model of the cross-bridge cycle, these data indicate that ionic strength and TMAO affect the apparent detachment rate constant. High ionic strength KCl solutions extract myosin heavy- and light-chains, and troponin C from rabbit fibers. This extraction is virtually abolished by TMAO. Natural zwitterions, such as TMAO, have been shown to protect proteins against destabilization by high salt or other denaturatants. Our data indicate that, even in the best of salts, destabilization of the actomyosin complex may play a role in the effect of high ionic strength on the contractile process.

Adenosine Triphosphate↗
PubMed1993

Contraction of developing avian heart muscle.

1. Developmental changes in contraction of chick heart show strong similarities with those of the mammalian myocardium. 2. Normalized twitch force of intact trabeculae from chick left ventricle increases most markedly during the 3-day period around the time of hatching. 3. At any age, elevation of extracellular [Ca2+] to 10-20 mM increases twitch force to a maximum. 4. Studies using membrane-free ("skinned") trabeculae demonstrate that the developmental increase in twitch force is paralleled by an increase in the maximal contractile capability of the muscle, that is probably due to proliferation of contractile proteins. 5. At all ages studied, maximal twitch force of intact trabeculae at 10-20 mM extracellular [Ca2+] is similar to maximal Ca(2+)-activated force of the trabeculae after skinning. 6. Calcium sensitivity of the contractile apparatus in chick heart decreases with development in parallel with isoform switching in troponin T. 7. The depressant effect of acidosis on calcium sensitivity of the contractile apparatus increases with development in parallel with isoform switching in troponin I. 8. As in mammalian heart, both acidosis and inorganic phosphate (Pi) depress force generation by the contractile machinery of chick heart.

Animals↗
PubMed1992

Ruthenium red affects the contractile apparatus but not sarcoplasmic reticulum Ca2+ release of skinned papillary muscle.

Ruthenium red has been shown to have a positive inotropic effect on isolated perfused hearts. The cellular mechanism of this action is not clear. Ruthenium red is able to block the Ca2+ release channel in isolated sarcoplasmic reticulum (SR) vesicle and reconstituted channel preparations. However, the effect of ruthenium red on SR Ca2+ release has not been studied in skinned cardiac muscle preparations. In the present study we investigated the actions of ruthenium red on both the characteristics of force generation by the contractile apparatus and Ca2+ release from the SR in chemically skinned rat papillary muscle. Ruthenium red (2 and 10 microM) significantly increased the Ca2+ sensitivity of the contractile apparatus (decreasing Ca2+ required for the half-maximal response from 1.56 +/- 0.04 microM to 1.46 +/- 0.05 microM) but had no effect on the maximal Ca(2+)-activated force in triton X-100 treated fibers. This result may suggest one explanation for the positive inotropic effect of ruthenium red on the heart. On the other hand, ruthenium red had no significant effect on either caffeine-induced Ca2+ release or Ca(2+)-induced Ca2+ release from the SR in saponin-skinned muscle fibers. Lack of a blocking effect on SR Ca2+ release by ruthenium red in skinned fibers suggests that the SR Ca2+ channels in intact preparations have characteristics that are different from those of either vesicular or reconstituted channel preparations.

Animals↗
PubMed1992

Inotropic influence of macrocyclic polyethers on tracheal smooth muscle.

Incubated guinea pig tracheal smooth muscle exhibited both positive and negative inotropic responses to a variety of crown ether analogs that ranged in size from 12-crown-4 to 30-crown-10 and included molecules whose lipophilicity was modified by the addition of benzo- and cyclohexo-substituents on the basic molecular framework. The inotropic influence of crown ethers may not only be due to their ionophoretic capabilities but may result from their ability to affect alterations in membrane physiology.

Animals↗
PubMed1992

Technical problems related to the analysis of the effects of inorganic phosphate on cardiac muscle.

1. We describe how potential artifacts (due to solution composition, buffering capacity of the bathing medium, size of the skinned fiber preparation, permeability of the sarcoplasmic reticulum (SR) vesicles, and proper Kd for Ca2+ of the fluorescent indicator used to measure Ca2+ transport can be avoided in order to determine the effects of inorganic phosphate (Pi, or any other ion) on maximum Ca2+ activated force (Fmax) and Ca2+ sensitivity of skinned cardiac muscle fibers, and Ca(2+)-ATPase activity and uptake properties of isolated cardiac SR-enriched vesicles. 2. To maintain the ionic strength of the bathing medium constant when adding Pi, other ions must be removed. We found that because some salts have a depressant effect on Fmax independent of increased ionic strength (e.g. KCl) while others do not (e.g. Na-acetate), the salt used to adjust ionic strength influences the measured depressant effect of Pi on Fmax. 3. The sensitivity to Ca2+ of the contractile apparatus depends on the sum of the [Na+] and [K+] in the bathing medium. However, we found that the effect of Pi on Ca2+ sensitivity was not significantly influenced by the small changes in the sum of [Na+] and [K+] that were associated with the addition of Pi. 4. The skinned fiber preparations were approximately cylindrical bundles with diameters ranging between 100 and 250 microns. We found that the effect of Pi on Fmax was not influenced by diffusion limitations over this range of bundle diameters. 5. The pH buffering capacity of the bathing solution affects Fmax at pH 6.6. We found that the buffering effect of Pi can influence the mechanical response of skinned fibers independent of a direct effect of Pi on the contractile apparatus when the buffering capacity of the control solution is low. 6. When the Ca(2+)-ATPase of isolated SR vesicles is activated by Ca2+ and MgATP, the vesicles accumulate Ca2+. Unless the vesicles are permeabilized with a Ca2+ ionophore (ionomycin) and the pH adequately buffered, maximum ATPase activity will be underestimated, the broadness of the curve relating Ca2+ to Ca(2+)-ATPase rate overestimated, and the sensitivity to Pi overestimated. 7. The ionic milieu of isolated SR vesicles changes the apparatus dissociation constant (Kd) of Ca(2+)-Fura-2, a fluorescent dye used to quantify SR Ca2+ transport rates. In order to accurately measure the inhibitory effect of Pi on Ca2+ uptake, the influence of Pi on the Kd of fura-2 for Ca2+ must be taken into account.

Animals↗
PubMed1991

Inositol trisphosphate enhances Ca2+ oscillations but not Ca(2+)-induced Ca2+ release from cardiac sarcoplasmic reticulum.

The role of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] in excitation-contraction coupling in cardiac muscle is still unclear, although many laboratories are beginning to assume a critical role for this putative second messenger. Earlier studies from this laboratory [Nosek et al. (1986) Am J Physiol 250:C807] found that Ins(1,4,5)P3 enhanced spontaneous Ca2+ release and the caffeine sensitivity of Ca2+ release from myocardial sarcoplasmic reticulum (SR) and proposed an increase in the Ca2+ sensitivity of the release as a possible mechanism. In order to clarify the physiological relevance of these actions of Ins(1,4,5)P3 and specifically to test the effect of Ins(1,4,5)P3 on the Ca2+ sensitivity of Ca2+ release, we compared the effects of Ins(1,4,5)P3 on Ca2+ oscillations and on Ca(2+)-induced Ca2+ release (CICR) from the SR in saponin-skinned rat papillary muscle. We found that: (a) 30 microM Ins(1,4,5)P3 enhanced the Ca2+ oscillations (measured by tension oscillations) from the rat cardiac SR, consistent with the previous report on guinea pig tissue; (b) both GTP and GTP[S] enhanced Ca2+ oscillations. The effect was not additive to that of Ins(1,4,5)P3 indicating that two different Ca(2+)-release pools do not exist in cardiac SR; (c) 30 microM Ins(1,4,5)P3 had no effect on the Ca2+ sensitivity of CICR; (d) Ins(1,4,5)P3 (up to 30 microM) had no effect on SR Ca2+ loading. The studies were performed in the presence of Cd2+ or 2,3-bisphosphoglycerate, agents that inhibit Ins(1,4,5)P3 hydrolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Ion-specific and general ionic effects on contraction of skinned fast-twitch skeletal muscle from the rabbit.

We used single fibers from rabbit psoas muscle, chemically skinned with Triton X-100 nonionic detergent, to determine the salts best suited for adjusting ionic strength of bathing solutions for skinned fibers. As criteria we measured maximal calcium-activated force (Fmax), fiber swelling estimated optically, and protein extraction from single fibers determined by polyacrylamide gel electrophoresis with ultrasensitive silver staining. All things considered, the best uni-univalent salt was potassium methanesulfonate, while a number of uni-divalent potassium salts of phosphocreatine, hexamethylenediamine N,N,N',N'-tetraacetic acid, sulfate, and succinate were equally acceptable. Using these salts, we determined that changes in Fmax correlated best with variations of ionic strength (1/2 sigma ci z2i, where ci is the concentration of ion i, and zi is its valence) rather than ionic equivalents (1/2 sigma ci magnitude of zi). Our data indicate that increased ionic strength per sc decreases Fmax, probably by destabilizing the cross-bridge structure in addition to increasing electrostatic shielding of actomyosin interactions.

Animals↗
PubMed1991

Changes in force and calcium sensitivity in the developing avian heart.

The aim of this study was to characterize the development of the contractile properties of intact and chemically skinned muscle from chicken heart and to compare these characteristics with those of developing mammalian heart reported by others. Small trabeculae were dissected from left ventricles of Arbor Acre chickens between embryonic day 7 and young adulthood (7 weeks post-hatching). At all ages, increasing extracellular calcium (0.45-3.6 mM) progressively increased twitch force of electrically stimulated trabeculae. Twitch force at 1.8 mM extracellular calcium, normalized to cross-sectional area, increased to a maximum at 1 day post-hatching, remained constant through 3 weeks post-hatching, but then decreased at 7 weeks post-hatching. The maximal calcium-activated force of trabeculae chemically skinned with Triton X-100 detergent increased to a maximum 2 days before the time of hatching and was not significantly changed up to 7 weeks post-hatching. Over the ages studied, average twitch force in 1.8 mM calcium was between 26 and 66% of maximal calcium-activated force after skinning, suggesting that the contractile apparatus is not fully activated during the twitch in normal Ringer. In skinned trabeculae, the calcium sensitivity of the contractile apparatus was higher in the embryo than in the young adult. These age-dependent changes in calcium sensitivity are correlated with isoform switching in troponin T. A decrease in pH from 7.0 to 6.5 decreased the calcium sensitivity of the contractile apparatus to a greater degree in skinned trabeculae from young adult hearts than in those from embryonic hearts. This change in susceptibility to acidosis is temporally associated with isoform switching in troponin I.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis↗
PubMed1991

Intracellular milieu changes associated with hypoxia impair sarcoplasmic reticulum Ca2+ transport in cardiac muscle.

The effects on sarcoplasmic reticulum (SR) Ca2+ transport of solutions mimicking the important intracellular milieu changes associated with short-term hypoxia (hypoxic solutions, as described by Kammermeier et al. J. Mol. Cell. Cardiol. 14: 267, 1982) were examined. SR Ca2+ content was estimated by measuring the magnitude of the caffeine-induced contracture in saponin-skinned rat papillary muscle. SR Ca2+ uptake was inhibited by hypoxic solutions only at loading times less than or equal to 30 s. This inhibition was primarily due to the increase in Pi. The hypoxic solutions had no effect on Ca(2+)-induced Ca2+ release from the SR. We also tested the effects of ATP-free (rigor) solutions that mimic the intracellular environment during late hypoxia and ischemia. Elevating Pi or ADP alone in rigor solution had no effect on SR Ca2+ content. However, elevating Pi and ADP (+/-Mg2+) produced a 44-48% reduction in SR Ca2+ content. This reduction is most likely due to reversal of the SR Ca2+ pump. We conclude that the changes in milieu with short-term hypoxia can depress contractility in intact cardiac muscle by inhibiting SR Ca2+ uptake. During long-term hypoxia or ischemia, these milieu changes can elevate intracellular Ca2+ by reversing the SR Ca2+ pump.

Adenosine Diphosphate↗
PubMed1990

Inositol trisphosphate has no direct effect on the contractile apparatus of skinned cardiac muscles.

Alpha-adrenoceptor stimulation produces a positive inotropic effect in heart muscle via mechanisms that are not well understood. The purpose of our study was to test the hypothesis that the increase in inositol 1,4,5 trisphosphate [Ins(1,4,5)P3] concentration that accompanies alpha stimulation contributes to the inotropic effect by increasing the calcium sensitivity of the contractile proteins, an effect which Ins(1,4,5)P3 has been shown to have in skeletal muscle. We determined the calcium sensitivity of the contractile apparatus of small, chemically skinned bundles from papillary muscles of rabbit, rat and dog hearts. These preparations were chosen because they exhibit a range of sensitivity to alpha agonists. In addition, we measured the calcium sensitivity of chemically skinned, single fibers from rabbit psoas muscle. All preparations were skinned with Triton X-100, a non-ionic detergent that disrupts the sarcolemmal, sarcoplasmic reticular, and mitochondrial membranes. In all cardiac preparations, we found that 38 microM Ins(1,4,5)P3 had no effect on either the calcium sensitivity or maximum calcium-activated force. Thus, there was no correlation between inotropic response to alpha stimulation and myocardial response to Ins(1,4,5)P3. On the other hand, the maximum calcium-activated force of skinned skeletal muscle was slightly increased by Ins(1,4,5)P3. Moreover, Ins(1,4,5)P3 significantly increased the sensitivity of these fibers to calcium.

Animals↗
PubMed1990

Inhibitory influence of phosphate and arsenate on contraction of skinned skeletal and cardiac muscle.

It has been widely observed that Pi decreases maximum calcium-activated force (Fmax) and calcium sensitivity of skinned skeletal and cardiac muscle. However, whether a particular ionic species of Pi (i.e., H2PO4-) is responsible for these effects is controversial. To clarify this issue, we examined the influence of Pi and its structural analogue arsenate (Asi) on contraction of skinned rabbit psoas (fast twitch), soleus (slow twitch), and cardiac papillary muscle. Asi decreased Fmax of all three muscles types to a greater extent than Pi. Both Pi and Asi decreased calcium sensitivity of psoas and cardiac muscles, with Asi having the greater effect. The effect of the protonated form of Pi and Asi on Fmax was evaluated by measuring the response to 30 mM total Pi or Asi at pH 7.4, 7.0, 6.6, and 6.2. In psoas fibers we found that both Pi and Asi were more effective in decreasing Fmax as the pH was lowered (i.e., as the concentration of the diprotonated forms increased). On the contrary, soleus and cardiac fibers did not exhibit this behavior. These differences in the effects of Pi and Asi on Fmax in psoas vs. cardiac and soleus muscles may be related to differences in their myosin heavy chains other than the binding site for the gamma-phosphate of ATP which appears to be conserved for all myosins.

Animals↗
PubMed1989

Changes of intracellular milieu with fatigue or hypoxia depress contraction of skinned rabbit skeletal and cardiac muscle.

1. Maximal calcium-activated force (Fmax) and calcium sensitivity were markedly decreased in detergent-skinned fibres from skeletal and cardiac muscle by solutions that mimicked the total milieu changes associated with fatigue and hypoxia. Further experiments determined the relative contribution of each of the individual changes in milieu. 2. Both Ca2+ sensitivity and Fmax of skeletal and cardiac fibres were decreased with increased [H+] or inorganic phosphate (Pi). These effects were greater in cardiac muscle. 3. Decreasing MgATP over the range observed with fatigue and hypoxia (6.8-4.7 mM) had no effect on Fmax or Ca2+ sensitivity of either muscle type. 4. Decreasing phosphocreatine (PCr: 15-1 mM) increased Fmax but had little effect on Ca2+ sensitivity in both muscle types. In cardiac fibres, the effect on Fmax could be mimicked by inhibition of endogenous creatine kinase. 5. ADP (0.7 mM) increased Fmax and Ca2+ sensitivity, while AMP (0.06 mM) slightly increased Fmax but had no effect on Ca2+ sensitivity of either skeletal or cardiac fibres. 6. Creatine (25 mM) had no significant effect on either Ca2+ sensitivity or Fmax of skeletal and cardiac muscle fibres. At higher levels (50 mM), however, creatine depressed Fmax and slightly altered Ca2+ sensitivity. 7. Thiophosphorylation of myosin P light chains (phosphorylatable light chains of myosin) in rabbit psoas fibres had no effect on Ca2+ sensitivity, yet slightly but significantly increased Fmax under fatigue conditions. 8. Reducing the affinity for ATP hydrolysis (by adding ADP, AMP and creatine) over the range calculated for fatigue/hypoxia (60-45 kJ/mol) produced the enhancement in Fmax expected from added ADP and AMP in cardiac but not skeletal muscle, indicating that changes in affinity influence Fmax of skeletal muscle. Reducing affinity produced little change in Ca2+ sensitivity of skeletal muscle. In contrast, the change produced in cardiac muscle was greater than that expected from addition of ADP and AMP; i.e. decreasing affinity increases calcium sensitivity of the heart. 9. Simple summation of all significant changes expected from each constituent altered by fatigue/hypoxia adequately predicted the observed changes in Fmax and Ca2+ sensitivity in both cardiac and skeletal muscle fibres with but one exception (the change in Ca2+ sensitivity of skeletal muscle at pH 7 was slightly overestimated).

Animals↗
PubMed1987

It is diprotonated inorganic phosphate that depresses force in skinned skeletal muscle fibers.

The increases in the intracellular concentrations of inorganic phosphate and hydrogen ion accompanying fatigue of skeletal muscle appear to be the most important metabolic changes associated with the decrease in contractile force. Experiments on chemically skinned single fibers from rabbit psoas muscle with pH ranging between 6 and 7.25 demonstrate that the depression of maximal calcium-activated force by inorganic phosphate correlates nicely with the concentration of the acidic (diprotonated) species. Therefore, in addition to the well-known depressant effect on the contractile machinery of lowering pH per se, any decrease of intracellular pH associated with fatigue further depresses force production by converting more of the total inorganic phosphate within the cell to the inhibitory diprotonated form.

Animals↗