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Inotropic agents. Introduction
J Mol
Cell
Cardiol24
0-14-7lWCWC~AL
(Supplement
I) (1992)
RRRRGETICS
DDRING VRRTRICULAR
FIBRILLATION:
ROLE OF CRLCIUM
Hideo Kusuoka, Eduardo Marban. Division of Cardiology, De artment of Medicine, The Johns Hopkins Universit School of Medicine, Baltimore, MD 212 B 5 U.S.A. To elucidate t ii e mechanism of the deterioration in energy metabolism during ventricular fibrillation (VF), the energy flux in myocardium was evaluated in isolated ferret hearts using 31P-NMR spectroscopy. VFwas induced either by digitalis toxicity (3Ofl strophanthidin) or by electrical stimulation. The flux in the reaction from phosphocreatine (PCr) to ATP catalyzed by creatine kinase, was measured using magnetization transfer, During digitalis-induced VF, energy-related phos hates showed changes similar to those during hypoxia: myocardial P concentration ([P P) increased (1.1 + 0.2 pmole/g wet wt in control, 7.5 + 0.4 during %F, (mean + SE, N-t), P
O-14-8
MYOCARDIAL GLUCOSE METABOLISM IS ALTERED IN THE RAT HEART BY b-HYDROXYBUTYRATE: DETECTION BY ‘H-, 13C. AND 3’P-NMR SPECTROSCOPY. John R. Forder, John C. Chatham, and Jerry D. Glickson. The Division of NMR Research, Department of Radiology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205-2195 USA Experiments were designed to investi ate the effect of p-hydroxybutyrate upon glucose metabolism; isolated rat hearts were studied using 13E - and SlP-NMR spectroscopy for simultaneous acquisition of biochemical and physiological data. Perfusate consisted of Krebs-Henseleit buffer (pH 7.4) containing l13C-glucose (5 mM) plus insulin (0.05 U/mL). Additional hearts were studied with p-hydroxybutyrate @HB; 11 mM) added to the perfusate (n=6). Three @lB hearts were subsequently infused with dichloroacetate (DCA, 5 mM), which stimulates pyruvate dehydrogenase. There were no changes in high energy phosphates, or intracellular pH, following addition of PHB, or DCA. Incorporation of label from 1-13C-glucose into glutamate was completely abolished in the presence of BHB, suggesting glucose does not enter the TCA cycle. Total glutamate doubled with pHB. 13C-NMR data suggest that fructose 1,6 diphosphate (FDP) accumulates in hearts after addition of f%hydroxybutyrate, something not seen in controls. In addition, the labelling rate from l-13C-glucose into glycogen increased two-fold in the presence of p-hydroxybutyrate, compared to hearts perfused with glucose alone. The addition of DCA decreased the rate of incorporation of glucose into glycogen to values not significantly different from hearts perfused with glucose alone. Addition of DCA also increased the labelling of lactate, increased the accumulation of FDP, and 13C-labelled glutamate was also detected, suggesting inhibition of glucose entry into the TCA cycle could be partially overcome by stimulation of pyruvate dehydrogenase.
o-15-1
INOTROPIC AGENTS. INTRODUCTION. Horatio E. Cingolani. Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Mgdicas, Universidad National de La Plata, 60 y 120, 1900 La Plata, Argentina. Tension development at a given muscle length is often referred to as contractility or the level of inotropic state. There are two general mechanisms through which the contractilit of the heart can be increased: 1) increase in the amplitude of the cytosolic Ca$+i transient and 2) increase in myofilament responsiveness to Caz+i. Positive or negative lusitropic alterations can accompany the inotropic changes as the result of altering APD either by K channel blockers of Na channel agonists. Phospholamban phosphorylation through protein kinase A, Ca z+-calmodulin or phosphatases alterations can modify SR uptake, loading and release and induce increase in contractility and relaxation. Decrease in intracellular pH (pHi) alters inotropic state by changing myofilament sensitivity but also by activation of Na/H exchanger which wi 1 in turn will produce an increase in Ca L. , induce increase in intracellular Nat, which and loading of SR. a receptor stimulation and endothelin are examples of positive The increase in contractility inotropic interventions without lusitropic alterations. induced by a receptor stimulation is depending on pHi and APD. The negative inotropic intervention produced by calcium channel blockers is accompanied by a negative lusitro ic alteration of unknown mechanisms. The link between contraction and relaxawith and without lusitropic changes. tion al Y ows to dissect inotropic interventions, 5.83
Cell
Cardiol24
0-14-7lWCWC~AL
(Supplement
I) (1992)
RRRRGETICS
DDRING VRRTRICULAR
FIBRILLATION:
ROLE OF CRLCIUM
Hideo Kusuoka, Eduardo Marban. Division of Cardiology, De artment of Medicine, The Johns Hopkins Universit School of Medicine, Baltimore, MD 212 B 5 U.S.A. To elucidate t ii e mechanism of the deterioration in energy metabolism during ventricular fibrillation (VF), the energy flux in myocardium was evaluated in isolated ferret hearts using 31P-NMR spectroscopy. VFwas induced either by digitalis toxicity (3Ofl strophanthidin) or by electrical stimulation. The flux in the reaction from phosphocreatine (PCr) to ATP catalyzed by creatine kinase, was measured using magnetization transfer, During digitalis-induced VF, energy-related phos hates showed changes similar to those during hypoxia: myocardial P concentration ([P P) increased (1.1 + 0.2 pmole/g wet wt in control, 7.5 + 0.4 during %F, (mean + SE, N-t), P
O-14-8
MYOCARDIAL GLUCOSE METABOLISM IS ALTERED IN THE RAT HEART BY b-HYDROXYBUTYRATE: DETECTION BY ‘H-, 13C. AND 3’P-NMR SPECTROSCOPY. John R. Forder, John C. Chatham, and Jerry D. Glickson. The Division of NMR Research, Department of Radiology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205-2195 USA Experiments were designed to investi ate the effect of p-hydroxybutyrate upon glucose metabolism; isolated rat hearts were studied using 13E - and SlP-NMR spectroscopy for simultaneous acquisition of biochemical and physiological data. Perfusate consisted of Krebs-Henseleit buffer (pH 7.4) containing l13C-glucose (5 mM) plus insulin (0.05 U/mL). Additional hearts were studied with p-hydroxybutyrate @HB; 11 mM) added to the perfusate (n=6). Three @lB hearts were subsequently infused with dichloroacetate (DCA, 5 mM), which stimulates pyruvate dehydrogenase. There were no changes in high energy phosphates, or intracellular pH, following addition of PHB, or DCA. Incorporation of label from 1-13C-glucose into glutamate was completely abolished in the presence of BHB, suggesting glucose does not enter the TCA cycle. Total glutamate doubled with pHB. 13C-NMR data suggest that fructose 1,6 diphosphate (FDP) accumulates in hearts after addition of f%hydroxybutyrate, something not seen in controls. In addition, the labelling rate from l-13C-glucose into glycogen increased two-fold in the presence of p-hydroxybutyrate, compared to hearts perfused with glucose alone. The addition of DCA decreased the rate of incorporation of glucose into glycogen to values not significantly different from hearts perfused with glucose alone. Addition of DCA also increased the labelling of lactate, increased the accumulation of FDP, and 13C-labelled glutamate was also detected, suggesting inhibition of glucose entry into the TCA cycle could be partially overcome by stimulation of pyruvate dehydrogenase.
o-15-1
INOTROPIC AGENTS. INTRODUCTION. Horatio E. Cingolani. Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Mgdicas, Universidad National de La Plata, 60 y 120, 1900 La Plata, Argentina. Tension development at a given muscle length is often referred to as contractility or the level of inotropic state. There are two general mechanisms through which the contractilit of the heart can be increased: 1) increase in the amplitude of the cytosolic Ca$+i transient and 2) increase in myofilament responsiveness to Caz+i. Positive or negative lusitropic alterations can accompany the inotropic changes as the result of altering APD either by K channel blockers of Na channel agonists. Phospholamban phosphorylation through protein kinase A, Ca z+-calmodulin or phosphatases alterations can modify SR uptake, loading and release and induce increase in contractility and relaxation. Decrease in intracellular pH (pHi) alters inotropic state by changing myofilament sensitivity but also by activation of Na/H exchanger which wi 1 in turn will produce an increase in Ca L. , induce increase in intracellular Nat, which and loading of SR. a receptor stimulation and endothelin are examples of positive The increase in contractility inotropic interventions without lusitropic alterations. induced by a receptor stimulation is depending on pHi and APD. The negative inotropic intervention produced by calcium channel blockers is accompanied by a negative lusitro ic alteration of unknown mechanisms. The link between contraction and relaxawith and without lusitropic changes. tion al Y ows to dissect inotropic interventions, 5.83