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Biomedical subjects

J F Clark

Publications and source records attributed to J F Clark.

At least 19 recordsLinked to original sources
PubMed2000

Intact smooth muscle metabolism: its responses to cyanide poisoning and pyruvate stimulation.

Smooth muscle mitochondria are unique in their compartmentalization of metabolism with the contractile proteins and putative role in cell fate choice. In this study we examine the relative and quantitative differences that smooth muscle mitochondria have with regard to cyanide inhibition. The effect of cyanide poisoning in the mitochondria of smooth muscle was examined in the intact porcine carotid artery and intact guinea pig stomach. The respiratory responses of these tissues were monitored in the presence of cyanide and following the addition of various metabolites. In HEPES buffer with 10 mM glucose as the substrate, it was found that the EC50 for cyanide inhibition was 0.11+/-0.02 and 0.14+/-0.02 mM in the pig carotid and guinea stomach respectively. We also found that the signaling metabolite, pyruvate could partially reverse this inhibition. With pyruvate (10 mM) as the substrate, the EC50 increased significantly to 6.52+/-0.11 (carotid artery) and 1.95+/-0. 30 (stomach) mM as well as being significantly different between the tissues. This apparent resistance to cyanide inhibition caused by pyruvate was lost when sodium bicarbonate buffer was used (EC50 in the presence of pyruvate of 0.13+/-0.04 and 0.25+/-0.04 for carotid and stomach respectively). HEPES buffer permitted pyruvate's protection from cyanide poisoning whereas bicarbonate buffer did not. The rate of respiration caused by pyruvate re-stimulation was not significantly different than control in the stomach (2.63+/-0.77 and 2.69+/-0.3??Mol O2/min/g dw respectively) but was significantly greater in the carotid artery. Therefore, smooth muscle with 10 mM pyruvate and 1 mM cyanide had a rate or respiration significantly greater than with 10 mM glucose alone (0.90+/-0.2 and 0.59+/-0. 06??Mol O2/min/g dw respectively). Using 31P NMR spectroscopy, we observed a complete normalisation of high energy phosphates and pH in the guinea pig stomach smooth muscle caused by pyruvate after cyanide poisoning. These results suggest that cyanide's toxicity of smooth muscle oxidative metabolism is affected by the buffer (HEPES versus Bicarbonate) and metabolic signalling molecules or substrates (pyruvate versus glucose) in which the tissues are exposed to as well as tissue to tissue variations.

Animals↗
PubMed2000

The presence of an extractable substance in the CSF of humans with cerebral vasospasm after subarachnoid haemorrhage that correlates with phosphatase inhibition.

The cellular events leading to cerebral vasospasm after subarachnoid haemorrhage are poorly understood, although an increase in smooth muscle myosin light chain phosphorylation has been observed. This study set out to determine if phosphatase inhibition may be involved in the pathological maintenance of tension observed during vasospasm. We found that 1 nM okadaic acid, a type 2A protein phosphatase inhibitor, elicited an increase in rate of O(2) consumption in the porcine carotid artery similar to that by cerebrospinal fluid (CSF) from vasospastic patients (CSF(V), n=5) (control 0.23+/-0.03, CSF(V) 0.84+/-0.16 and okadaic acid 0.85+/-0.02 micromol min(-1) g dwt(-1)). It was also observed that phosphatase inhibition with 1 nM okadaic acid significantly slowed relaxation after a stretch in a similar fashion to CSF(V) haemorrhage. CSF from vasospastic subarachnoid haemorrhage patients, but not from those without vasospasm, contains an extractable substance which modulates myosin light chain phosphorylation in vitro. A phosphatase preparation obtained from the porcine carotid artery dephosphorylated 63+/-2% of the phosphorylated (MLC(20)) substrate in vitro, and non-vasospastic CSF treated enzyme dephosphorylated 60+/-2.6%. Okadaic acid inhibited phosphatase dephosphorylated only 7.5+/-1% of the substrate where CSF(V) treated enzyme dephosphorylated 22+/-2.8% of the substrate. We conclude that inhibition of smooth muscle phosphatase may be involved in the mechanisms associated with cerebral vasospasm after subarachnoid haemorrhage.

Animals↗
PubMed2000

The effects of anti-hypertensive therapy on the structural, mechanical and metabolic properties of the rat aorta.

The vascular system exhibits altered growth, calcium responses and metabolism during hypertension. To relate such changes, we compared histological, tension and metabolic responses in the aorta from 32-week-old spontaneously hypertensive rats (SHRs), normotensive Wistar-Kyoto (WKY) rats, and SHRs treated with Verapamil (V) and ACE-inhibitor, Trandolapril (T) as well as a combination of the two treatments (C). Vascular hypertrophy was apparent in the SHRs. Contractile responses induced by 50 mmol/1 KCl and 2.5 mmol/1 Ca2+ were significantly lower in the SHR (64.4 mN/mm2 vs. 49.2 mN/mm2), but an associated increase in Ca2+ -sensitivity (EC50 of extracellular Ca2+ (mumol/1): SHR, 456 vs. WKY, 616) normalised tension generating ability. All treatments led to significant decreases in blood pressure, although only T and C treated animals became normotensive with concomitant normalisation of vascular hypertrophy. An increase in oxygen consumption was apparent in the SHR aorta, which was associated with significant differences in the activities of key metabolic enzymes. Anti-hypertensive treatment normalised many of the metabolic parameters, with the C therapy being the most efficacious. We conclude that the treatment of hypertension by combined therapy leads to a better normalisation of structural, contractile, and metabolic parameters in the SHR, than either treatment alone and that metabolic changes with the pathology are resolved with appropriate therapy.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2000

The effects of placental extracts from normotensive and preeclamptic women on vasoconstriction and oxidative metabolism.

OBJECTIVE: A circulating factor derived from the placenta has been implicated in the pathogenesis of preeclampsia. The aim of this study was to determine whether placental extracts from normotensive women and women with preeclampsia increase oxidative metabolism and histamine-induced vasoconstriction in porcine carotid artery. STUDY DESIGN: Placental extracts from normotensive women and women with preeclampsia were applied to porcine carotid artery, and oxidative metabolism was measured. Histamine-induced isometric force responses were also determined in the absence and presence of placental extracts. RESULTS: Application of placental extracts to porcine carotid artery caused a fall in oxygen tension, which reflects increased consumption. Extracts from placentas taken from women with preeclampsia caused a greater fall than those from normotensive women (0.117 +/- 0.026 vs 0.018 +/- 0.0024 micromol oxygen per milligram; P < or =.01). Histamine-induced contractions were potentiated by extracts from preeclampsia but not from those of women without hypertension. The maximal steady-state force values were 13,137 +/- 3647, 12,921 +/- 3684, and 21,673 +/- 7189 N/m(-2) for control, normotensive, and preeclamptic samples at 10-micromol/L histamine (P < or =.05, compared with control placental extracts). CONCLUSIONS: Placental extracts from women with preeclampsia cause a greater stimulation of porcine artery oxygen consumption and exacerbation of histamine-induced vasoconstriction than extracts from normotensive women.

Animals↗
PubMed1999

Metabolic consequences of the cytochrome c oxidase deficiency in brain of copper-deficient Mo(vbr) mice.

Biochemical micromethods were used for the investigation of changes in mitochondrial oxidative phosphorylation associated with cytochrome c oxidase deficiency in brain cortex from Mo(vbr) (mottled viable brindled) mice, an animal model of Menkes' copper deficiency syndrome. Enzymatic analysis of cortex homogenates from Mo(vbr) mice showed an approximately twofold decrease in cytochrome c oxidase and a 1.4-fold decrease in NADH:cytochrome c reductase activities as compared with controls. Assessment of mitochondrial respiratory function was performed using digitonin-treated homogenates of the cortex, which exhibited the main characteristics of isolated brain mitochondria. Despite the substantial changes in respiratory chain enzyme activities, no significant differences were found in maximal pyruvate or succinate oxidation rates of brain cortex homogenates from Mo(vbr) and control mice. Inhibitor titrations were used to determine flux control coefficients of NADH:CoQ oxidoreductase and cytochrome c oxidase on the rate of mitochondrial respiration. Application of amobarbital to titrate the activity of NADH:CoQ oxidoreductase showed very similar flux control coefficients for control and mutant animals. Alternately, titration of respiration with azide revealed for Mo(vbr) mice significantly sharper inhibition curves than for controls, indicating a more than twofold elevated flux control coefficient of cytochrome c oxidase. Owing to the reserve capacity of respiratory chain enzymes, the reported changes in activities do not seem to affect whole-brain high-energy phosphates, as observed in a previous study using 31P NMR.

Animals↗
PubMed1998

Vascular smooth muscle oxygen consumption is reversibly stimulated by sera from women with preeclampsia.

OBJECTIVE: Preeclampsia is a complication of pregnancy that causes maternal vasoconstriction and hypertension. The disease may progress to eclampsia, which is thought to be related to cerebral vasospasm. Although there is evidence for more than one circulating factor that causes endothelial cell dysfunction in preeclampsia, little work has focused on the possibility that vascular smooth muscle function might be directly stimulated by a circulating factor. The aim of this study was to determine whether such a factor or factors could be detected by the vessels. STUDY DESIGN: Excessive vascular smooth muscle oxygen consumption was used as a screen for metabolic stimulation because pathologic arterial constriction would require oxidative metabolism to generate adenosine triphosphate. De-endothelialized porcine carotid artery (a well-validated model of human arterial contractile function) was exposed to sera from patients with preeclampsia (1:30 dilution) in a sealed chamber with an oxygen electrode, and the rate of oxygen consumption by the tissue was measured. Comparisons with the effects of sera from matched normal pregnant patients and from nonpregnant women were made. RESULTS: Exposure of vascular smooth muscle to sera from women with preeclampsia for 90 minutes resulted in greater oxygen consumption by the tissue (0.66 +/- 0.16 micromol O2 /min per gram of dry weight) than did exposure to sera of matched pregnant and nonpregnant control subjects (0.34 +/- 0.08 micromol O2 /min per gram of dry weight, P <.001, and 0.29 +/- 0.03 micromol O2 /min per gram of dry weight, P <.001, respectively). This stimulation was completely reversed by rinsing. CONCLUSIONS: There is a factor in the circulation of women with preeclampsia that has the reversible effect on vascular smooth muscle of accelerating oxygen consumption. We discuss the implications of this observation in terms of known aspects of vascular smooth muscle contractile function.

Animals↗
PubMed1998

Cocaine use as a risk factor for abdominal pregnancy.

Failure to diagnose abdominal pregnancies can have disastrous morbidity/mortality consequences for mother and fetus. To make the diagnosis of abdominal pregnancy requires that the physician have a high index of suspicion and that he or she have a good understanding of the risk factors of abdominal pregnancy. This article presents data suggesting that maternal cocaine use is a risk factor for abdominal pregnancy, reviews the literature on the maternal/fetal effects of maternal cocaine use and the risk factors of abdominal pregnancy, and analyzes 55 cases of abdominal pregnancy. Maternal cocaine use correlated with a 20% rate of increase in the incidence of abdominal pregnancy compared with the 70% rate of decrease in the "before cocaine" time period. Recommendations are offered for management.

Adult↗
PubMed1998

Theoretical modelling of some spatial and temporal aspects of the mitochondrion/creatine kinase/myofibril system in muscle.

After discussing approaches to the modelling of mitochondrial regulation in muscle, we describe a model that takes account, in a simplified way, of some aspects of the metabolic and physical structure of the energy production/usage system. In this model, high-energy phosphates (ATP and phosphocreatine) and low energy metabolites (ADP and creatine) diffuse between the mitochondrion and the myofibrillar ATPase, and can be exchanged at any point by creatine kinase. Creatine kinase is not assumed to be at equilibrium, so explicit account can be taken of substantial changes in its activity of the sort that can now be achieved by transgenic technology in vivo. The ATPase rate is the input function. Oxidative ATP synthesis is controlled by juxtamitochondrial ADP concentration. To allow for possible functional 'coupling' between the components of creatine kinase associated with the mitochondrial adenine nucleotide translocase and the myofibrillar ATPase, we define parameters phi and psi that set the fraction of the total flux carried by ATP rather than phosphocreatine out of the mitochondrial unit and into the ATPase unit, respectively. This simplification is justified by a detailed analysis of the interplay between the mitochondrial outer membrane porin proteins, mitochondrial creatine kinase and the adenine nucleotide translocase. As both processes of possible 'coupling' are incorporated into the model as quantitative parameters, their effect on the energetics of the whole cell model can be explicitly assessed. The main findings are as follows: (1) At high creatine kinase activity, the hyperbolic relationship of oxidative ATP synthesis rate to spatially averaged ADP concentration at steady state implies also a near-linear relationship to creatine concentration, and a sigmoid relation to free energy of ATP hydrolysis. At high creatine kinase activity, the degree of functional coupling at either the mitochondrial or ATPase end has little effect on these relationships. However, lowering the creatine kinase activity raises the mean steady state ADP and creatine concentrations, and this is exaggerated when phi or psi is near unity (i.e. little coupling). (2) At high creatine kinase activity, the fraction of flow at steady state carried in the middle of the model by ATP is small, unaffected by the degree of functional coupling, but increases with ADP concentration and rate of ATP turnover. Lowering the creatine kinase activity raises this fraction, and this is exaggerated when psi or psi is near unity. (3) Both creatine and ADP concentrations show small gradients decreasing towards the mitochondrion (in the direction of their net flux), while ATP and phosphocreatine concentration show small gradients decreasing towards the myosin ATPase. Unless phi = psi = 0 (i.e. complete coupling), there is a gradient of net creatine kinase flux that results from the need to transform some of the 'adenine nucleotide flux' at the ends of the model into 'creatine flux' in the middle; the overall net flux is small, but only zero if phi = psi. A reduction in cytosolic creatine kinase activity decreases ADP concentration at the mitochondrial end and increases it at the ATPase end. (4) During work-jump transitions, spatial average responses exhibit exponential kinetics similar to those of models of mitochondrial control that assume equilibrium conditions for creatine kinase. (5) In response to a step increase in ATPase activity, concentration changes start at the ATPase end and propagate towards the mitochondrion, damped in time and space. This simplified model embodies many important features of muscle in vivo, and accommodates a range of current theories as special cases. We end by discussing its relationship to other approaches to mitochondrial regulation in muscle, and some possible extensions of the model.

Adenosine Diphosphate↗
PubMed1997

Consequences of metabolic inhibition in smooth muscle isolated from guinea-pig stomach.

1. In smooth muscle isolated from the guinea-pig stomach, cyanide (CN) and iodoacetic acid (IAA) were applied to block oxidative phosphorylation and glycolysis, respectively. Effects of IAA on generation of spontaneous mechanical and electrical activities were systematically investigated by comparing those of CN. Spontaneous activity ceased in 10-20 min during applications of 1 mM IAA. On the other hand, application of 1 mM CN also reduced the spontaneous activity, but never terminated it. In the presence of CN the negativity of the resting membrane potential was slightly reduced. 2. When spontaneous activity ceased with IAA, the resting membrane potential was not significantly affected. Also, before ceasing, the amplitude and duration of the spontaneous electrical activity were significantly reduced. The amplitude of the electrotonic potential was, however, not changed by IAA. Further, glibenclamide did not prevent the effects of IAA. These results suggest that, unlike cardiac muscle, activation of metabolism-dependent K+ channels in stomach smooth muscle does not seem to play a major role in reducing and terminating spontaneous activity during metabolic inhibition. 3. Carbachol-induced contraction transiently increased, and subsequently decreased gradually during application of IAA. 4. After 50 min application of IAA, when there was no spontaneous activity, the concentrations of phosphocreatine (PCr) and ATP measured with 31P nuclear magnetic resonance decreased to 60 and 80% of the control, respectively, while inorganic phosphate (Pi) concentration paradoxically fell to below detectable levels. During subsequent prolonged application of IAA, high-energy phosphates steadily decreased. On the other hand, after 50 min CN application, [PCr] and [ATP] decreased to approximately 30 and 80% of the control, respectively, while [Pi] increased by 2.6-fold. 5. In the presence of either CN or IAA, spontaneous mechanical and electrical activities were reduced or eliminated, although amounts of high-energy phosphates sufficient to contract smooth muscle remained. It can be postulated that some mechanism(s) related to energy metabolism, but not including ATP-sensitive K+ channels, plays an important role in generating spontaneous activity in guinea-pig stomach smooth muscle. During metabolic inhibition the energy metabolism-dependent mechanism(s) would preserve high-energy phosphates, and consequently cell viability, by stopping spontaneous activity.

Adenosine Triphosphate↗
PubMed1997

ADP-regenerating enzyme systems in mitochondria of guinea pig myometrium and heart.

Any enzyme or enzyme system that produces ADP in proximity to the mitochondria may be capable of stimulating respiration. Hexokinase (HK), adenylate kinase (AK), and mitochondrial creatine kinase (Mi-CK) all catalyze reactions that produce ADP and thus may play a role in cellular nucleotide metabolism or control of mitochondrial oxidative phosphorylation. Respiratory characteristics and enzyme activities of mitochondria simultaneously isolated from heart and uterus of the gravid guinea pig were compared. The abilities of AMP, glucose, and creatine to stimulate mitochondrial respiration via AK, HK, and Mi-CK systems, respectively, were examined. Although the uterine Mi-CK activity is low compared with the values found in heart, the activities of HK and AK were significantly greater. Furthermore, the abilities of HK and AK to stimulate respiration (functional activity) were greater in the uterine mitochondria. Indeed, the activity of AK was sufficient to generate maximal (state 3) respiration. The apparent Michaelis constant (Km) for ADP to stimulate respiration in the isolated uterine mitochondria was significantly different from that of the heart mitochondria (9.6 +/- 0.9 and 5.1 +/- 1 microM ADP, respectively). It is concluded that uterine mitochondria can use HK and AK systems in addition to the CK system in enhancing local ADP concentration, which may aid in the mitochondrial responses to energetic demands.

Adenosine Diphosphate↗
PubMed1997

A theoretical model of some spatial and temporal aspects of the mitochondrion creatine kinase myofibril system in muscle.

We describe a model of mitochondrial regulation in vivo which takes account of spatial diffusion of high-energy (ATP and phosphocreatine) and low-energy metabolites (ADP and creatine), their interconversion by creatine kinase (which is not assumed to be at equilibrium), and possible functional 'coupling' between the components of creatine kinase associated with the mitochondrial adenine nucleotide translocase and the myofibrillar ATPase. At high creatine kinase activity, the degree of functional coupling at either the mitochondrial or ATPase end has little effect on relationships between oxidative ATP synthesis rate and spatially-averaged metabolite concentrations. However, lowering the creatine kinase activity raises the mean steady state ADP and creatine concentrations, to a degree which depends on the degree of coupling. At high creatine kinase activity, the fraction of flow carried by ATP is small. Lowering the creatine kinase activity raises this fraction, especially when there is little functional coupling. All metabolites show small spatial gradients, more so at low cytosolic creatine kinase activity, and unless there is near-complete coupling, so does net creatine kinase flux. During workjump transitions, spatial-average responses exhibit near-exponential kinetics as expected, while concentration changes start at the ATPase end and propagate towards the mitochondrion, damped in time and space.

Animals↗
PubMed1996

The utilisation of creatine and its analogues by cytosolic and mitochondrial creatine kinase.

We have investigated the utilisation of four analogues of creatine by cytosolic Creatine Kinase (CK), using 31P-NMR in the porcine carotid artery, and by mitochondrial CK (Mt-CK), using oxygen consumption studies in isolated heart mitochondria and skinned fibers. Porcine carotid arteries were superfused for 12 h with Krebs-Henseleit buffer at 22 degrees C, containing 11 mM glucose as substrate, and supplemented with either 20 mM beta-guanidinopropionic acid (beta-GPA), methyl-guanidinopropionic acid (m-GPA), guanidinoacetic acid (GA) or cyclocreatine (cCr). All four analogues entered the tissue and became phosphorylated by CK as seen by 31 P-NMR, Inhibition of oxidative metabolism by 1 mM cyanide after accumulation of the phosphorylated analogue resulted in the utilisation of PCr, beta-GPA-P, GA-P and GA-P over a similar time course (approximately 2 h), despite very different kinetic properties of these analogues in vitro. cCr-P was utilised at a significantly slower rate, but was rapidly dephosphorylated in the presence of both 1 mM iodoacetate and cyanide (to inhibit both glycolysis and oxidative metabolism respectively). The technique of creatine stimulated respiration was used to investigate the phosphorylation of the analogues by Mt-CK, Isolated mitochondria were subjected to increasing [ATP], whereas skinned fibres received a similar protocol with increasing [ADP]. There was a significant stimulation of respiration by creatine and cCr in isolated mitochondria (decreased K(m) and increased Vmax vs control), but none by GA, mGPA or beta-GPA (also in skinned fibres), indicating that these latter analogues were not utilised by Mt-CK. These results demonstrate differences in the phosphorylation and dephosphorylation of creatine and its analogues by cytosolic CK and Mt-CK in vivo and in vitro.

Adenosine Diphosphate↗
PubMed1996

Increase of flux control of cytochrome c oxidase in copper-deficient mottled brindled mice.

The brindled mottled mouse (Mobr), an animal model of the Menkes' copper deficiency syndrome, was used for the investigation of changes in respiratory flux control associated with cytochrome c oxidase deficiency in muscle. Enzymatic analysis of cardiac and skeletal muscles showed an approximately 2-fold decrease in cytochrome c oxidase activity of brindled mutants in both types of muscles as compared with controls. The activities of NADH-cytochrome c oxidoreductase (respiratory chain segment I-III) and succinate-cytochrome c oxidoreductase (segment II-III) were normal. Assessment of mitochondrial respiratory function was performed using chemically skinned musculus quadriceps or heart muscle fibers isolated from control and brindled mottled mice. In skeletal muscle, there was no difference found in maximal rates of respiration. In the Mobr hearts, this parameter was slightly lower than control. Alternately, the determination of flux control coefficients of cytochrome c oxidase performed by a step by step inhibition of respiration with increasing concentrations of azide or cyanide revealed significantly sharper inhibition curves for brindled mice than for control, indicating more than 2-fold elevated flux control coefficients of cytochrome c oxidase. This investigation proved essential in characterizing the metabolic effect of a cytochrome c oxidase deficiency. We conclude, therefore, that application of metabolic control analysis can be a valuable approach to study defects of mitochondrial oxidative phosphorylation.

Animals↗
PubMed1996

Effects of treatment of spontaneously hypertensive rats with the angiotensin-converting enzyme inhibitor trandolapril and the calcium antagonist verapamil on the sensitivity of glucose metabolism to insulin in rat soleus muscle in vitro.

We measured the sensitivity of glucose metabolism to insulin in soleus muscle preparations isolated from spontaneously hypertensive (SH) rats and normotensive age-matched Wistar-Kyoto (WKY) rats. SH rats were treated with the angiotensin-converting enzyme (ACE) inhibitor trandolapril (1 mg/kg) and/or a second antihypertensive drug, the calcium antagonist verapamil, alone (100 mg/kg) or as combination therapy (50 mg/kg). Treatment of SH rats with trandolapril or trandolapril in combination with verapamil for 6 weeks normalized the blood pressure. The estimated concentration of insulin required for half-maximal stimulation of glycogen synthesis (i.e., EC50 values) was approximately 500 microU/ml for muscles from both WKY and SH rats. This value is five times higher than the value obtained from soleus muscle preparations isolated from insulin-sensitive Wistar rats. This indicates that glycogen synthesis is insensitive to insulin in SH and WKY rat soleus muscle. Treatment of SH rats with trandolapril with or without verapamil improved the sensitivity of glycogen synthesis to insulin in soleus muscle. Further experiments investigated whether acute exposure (1 h) of insulin-sensitive skeletal muscle with either trandolaprilat (the active metabolite of trandolapril) or bradykinin (levels of which may be raised by ACE inhibition) could affect the insulin-stimulated rate of glucose metabolism. These results show that both trandolaprilat and bradykinin caused a small but significant increase in the rates of glucose metabolism. In conclusion, 1) SH and WKY rat skeletal muscle was insulin resistant, 2) chronic treatment of SH rats with trandolapril with or without verapamil normalized blood pressure and improved the response of glycogen metabolism to insulin, and 3) bradykinin and trandolaprilat acutely caused a small but significant increase in the rate of glycogen synthesis to a submaximal physiological concentration of insulin.

Angiotensin-Converting Enzyme Inhibitors↗