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S Bartel

Publications and source records attributed to S Bartel.

52 records · Page 3Linked to original sources
PubMed1986

Oscillation of cyclic AMP with the heart cycle of the canine myocardium in situ.

Oscillations of cyclic AMP with the cardiac cycle were demonstrated in the canine heart in situ. For tissue sampling an ECG(R-wave)-triggered, automatically working push-freeze-drill apparatus was employed which allowed intraventricular cryobiopsies from the left ventricular muscle of anaesthetized open-chest dogs. The nucleotide cyclic AMP oscillated with the cardiac cycle during normal working conditions, the higher cyclic AMP values occurring during systole. Cyclic GMP was assayed to be without oscillatory changes during the contraction-relaxation cycle of the heart.

Animals↗
PubMed1986

Metabolic and contractile changes in ischaemic rat hearts after isoproterenol administration: effect of reperfusion.

The effect of isoproterenol and of ischaemia followed by reperfusion was studied in isolated perfused rat heart. Whereas after an interval of 5 min of ischaemia the mechanical and biochemical responses to catecholamine were drastically reduced, reperfusion for 1 min normalized the cardiac reactivity. After prolonged ischaemia and reperfusion the hormone-induced rise in cyclic AMP and activation of cyclic AMP dependent protein kinase remains reduced. It is suggested that these changes might be of importance for cardiac protection during a transient ischaemic period.

Animals↗
PubMed1986

Adrenergic regulation of the acute ischaemic myocardium: facts, interpretations and consequences.

Anoxic stress is accompanied by activation of the central and peripheral sympathetic nervous system resulting in a high local catecholamine concentration. The authors studied how myocardial cells cope with the high level of catecholamines under ischaemic conditions. The beta-adrenoceptor-adenylate cyclase system (AC) was investigated in different models of ischaemia and anoxia (global ischaemia, low-perfused hearts, coronary artery ligation) in rat hearts. It was shown that beta-receptor function is not changed up to 40 min of ischaemia. Myocardial AC function was depressed in the total ischaemic myocardium but not in the low-perfused hearts indicating a non-uniform alteration of AC function. Reduced AC activity was completely reversible by aerobic perfusion as long as the ischaemic period did not exceed 20 min. Depression of AC function during severe ischaemia was avoided by reducing Ca2+ in the extracellular fluid and by pretreatment with Ca2+ channel blockers (verapamil). Depression of AC function during severe ischaemia is caused mainly by increased intracellular Ca2+ which inhibits AC at its catalytic site. Myocardial ischaemia alters the response of myocardial cells to catecholamines and other activators of the AC system. This alteration is time-limited and turns damage to AC function from reversible to irreversible after prolongation of ischaemia to more than 30 min.

Adenylyl Cyclases↗
PubMed1985

Reversible inhibition of adenylate cyclase activity in the ischemic myocardium.

Adenylate cyclase (AC) function was studied in homogenate and particulate preparations of ischemic rat heart obtained from three models: anoxic-ischemic incubations, coronary artery ligation, and global low-flow perfusion of isolated hearts. Both basal activity and the function of AC measured in the presence of NaF (8 X 10(-3)M), Gpp(NH)p (10(-5)M), and L-(-)-isoprenaline (10(-8)-10(-4)M) were reduced to 50% of the control value in homogenates of hearts incubated under anoxic-ischemic conditions for 10 min. Comparable results were obtained with homogenates from the ischemic area 20 min after coronary artery ligation in anesthetized open-chest rats with artificial ventilation. Reduced AC activity of the anoxic-ischemic hearts was completely reversible by aerobic reperfusion, provided the ischemic period did not exceed 20 min. AC activity in homogenates of isolated hearts perfused at low-flow was not changed, indicating a nonuniform alteration of AC system in nonperfused and low-flow perfused areas of the ischemic heart. Depression of myocardial AC function during severe ischemia was avoided by reducing Ca2+ in the incubation buffer, in combination with addition of EGTA during the homogenization step, and by pretreating the animals with verapamil. It is suggested that the depressed AC function is caused mainly by an increase in intracellular Ca2+, which inhibits the enzyme at its catalytic site. A negative feedback control of AC function by Ca2+ is postulated that may operate especially in the ischemic myocardium.

Adenylyl Cyclases↗
PubMed1985

Assay of cyclic AMP-dependent protein kinase activity in canine myocardium: effect of coronary artery ligation on the cytosolic enzyme.

A procedure for the determination of the activation state of cyclic AMP-dependent protein kinase (cAMP-PK) in the cytosolic fraction of dog myocardium was derived from existing assays of this enzyme in tissues, a new element being the absence of added sodium chloride throughout the procedure. About 2/3 of the total cAMP-PK in normal dog ventricular myocardium was found to be present in the cytosolic (supernatant) fraction, the remaining 1/3 being particle-bound. The isoenzyme profile in the cytosolic fraction as determined by DEAE-cellulose chromatography revealed the presence of nearly equal amounts of the type I and type II isoenzymes. This distribution was also evident in experiments in which the RI and RII regulatory subunits were photoaffinity labeled with 8-azido- [32P] cAMP. Ligation of the left circumflex coronary artery in anesthetized open-chest dogs kept under artificial respiration caused increases in the cAMP-PK activity ratio (-cAMP/+cAMP) from a control value of 0.11 to 0.26 and 0.22, respectively, in the ischemic and in a nonischemic area of the left ventricle. This effect was clearly evident 2 min after ligation and was still observable in the ischemic area after 20 min. It was associated with increases in cAMP levels and in the activity ratio (-5' -AMP/+5' -AMP) of glycogen phosphorylase in the ventricular tissues. Pretreatment of the dogs with (+/-)-propranolol (2 mg/kg) abolished the cAMP and cAMP-PK responses, while the phosphorylase activity ratio remained elevated.

Aerobiosis↗
PubMed1983

Cyclic nucleotides and changes in protein kinase activity ratio in the ischemic and nonischemic myocardium.

Following coronary artery ligation (CAL), levels of cAMP and the activity ratio of cAMP-dependent protein kinase, of phosphorylase kinase, and of phosphorylase are significantly elevated in both ischemic and nonischemic areas of the canine left ventricle. The aerobic level of cAMP was found to be 0.4 to 0.6 pmol/mg myocardium only after a precooled clamp or a cryobiopsy device was employed to guarantee tissue freezing in situ. Maximal changes in response to ischemia are observed within 2 min in both parts of the heart. Twenty minutes after the onset of ischemia, different responses have been found in the nonischemic and ischemic tissue. Whereas the levels of cAMP and the activity ratio of protein kinase, of phosphorylase kinase, and of phosphorylase returned to aerobic values in the nonischemic area, these parameters remained elevated in the ischemic area. The changes in the levels of myocardial cAMP and in the cAMP-dependent protein kinase activity ratio following CAL could be prevented by propranolol.

Animals↗
PubMedDate not supplied

Protein phosphorylation in isolated trabeculae from nonfailing and failing human hearts.

Disturbances in the cAMP production during beta-adrenergic stimulation and alterations of Ca2+ transport controlling proteins and their regulation in the sarcoplasmic reticulum might be involved in the pathogenesis of the failing human heart. Thus, we investigated the cAMP-mediated phosphorylation of phospholamban, troponin I and C-protein in electrically driven, intact isolated trabeculae carneae from nonfailing and failing (NYHA IV) human hearts in parallel to contractile properties on the same tissue samples. The increase in force of contraction induced by isoproterenol (0.2 microM) or pimobendan (100 microM), a phosphodiesterase inhibitor, was diminished in the failing human hearts compared to nonfailing hearts by 49% and 36%, respectively. Concomitantly the isoproterenol-induced phosphorylation (pmol P/mg homogenate protein) of phospholamban, troponin I and C-protein was reduced from 13.0 +/- 2.4 (n = 4), 30.5 +/- 1.5 (n = 5) and 11.0 +/- 1.3 (n = 5) in the nonfailing heart to 5.2 +/- 0.6 (n = 13), 14.6 +/- 2.2 (n = 16) and 7.1 +/- 1.0 (n = 6) in the failing human heart, respectively. Pimobendan changed the phosphorylation state of these proteins similar to isoproterenol. The fact that combined addition of both agents or dibuturyl cAMP (1 mM) alone restored the phosphorylation capacity as observed in the control groups indicates that i) a reduced cAMP generation is related to the reduced phosphorylation of regulatory phosphoproteins located in the sarcoplasmic reticulum and contractile apparatus e.g. phospholamban, troponin I and C-protein, that ii) there is a relationship between protein phosphorylation state and contractile activity and that iii) no changes in the respective content of phosphoproteins are involved in the limitation of cAMP-mediated inotopic activity in the failing human heart.

Adolescent↗
PubMedDate not supplied

HSP25 in isolated perfused rat hearts: localization and response to hyperthermia.

Recent investigations concentrate on the correlation between the myocardial expression of the inducible 70-kDa heat shock protein (HSP70i) by different stress conditions and its possible protective effects. Only few studies have focused on the involvement of small heat shock proteins in this process. We analyzed the location of the small heat shock protein HSP25 in isolated cardiomyocytes as well as its location and induction in isolated perfused hearts of rats. By immunofluorescence microscopy HSP25 was found to colocalize with actin in the I-band of myofibrils in cardiomyocytes of isolated perfused hearts as well as in isolated neonatal and adult cardiomyocytes. Hyperthermic perfusion of isolated hearts for 45 min resulted in modulation of different parameters of heart function and in induction of HSP25 is constitutively expressed even in normothermic perfused (44-46 degrees C) were lethal with respect to the contractile function of the hearts. Compared to control hearts perfused at 37 degrees C, significant increases during hyperthermic perfusion at 42 degrees C and 43 degrees C were obtained for heart rate, contraction velocity and relaxation velocity. In response to hyperthermia at 43 degrees C and after subsequent normothermic perfusion for 135 min at 37 degrees C, left to control values immediately after the period of heat treatment. HSP25 is constitutively expressed even in normothermic perfused hearts as shown by Western blotting. Hyperthermia increased the content of HSP25 only in the left ventricular tissue. In contrast, HSP70i was strongly induced in all analyzed parts of the myocardium (left ventricle, right ventricle, septum). Our findings suggest a differential regulation of HSP25 and HSP70i expression in response to hyperthermia in isolated perfused hearts. The constitutively expressed HSP25 seems to be located adjacent to the myofibrils which implies a specific role of this protein even under unstressed conditions for the contractile function of the myocardium.

Animals↗
PubMedDate not supplied

G proteins, adenylyl cyclase and related phosphoproteins in the developing rat heart.

The postnatal alterations of the composition of alpha subunit isoforms (Gi alpha c, Gi alpha 3, G(o) alpha, and Gq alpha) of G proteins, the adenylyl cyclase activity as well as of cAMP-regulated phosphoproteins e.g. troponin I and phospholamban were investigated in the ventricular tissue of 1, 7, 30 days old rats. Quantitative immunodetection revealed a 5.7-fold decrease in Gi alpha 3 at 30th postnatal day compared with the postnatal day 1 and up to 15-fold at 4 months. The amounts of Gq alpha and G(o) alpha as well as the G beta subunits were found to be higher in the earlier life period compared to the adult. In contrast, the content of Gs alpha was uneffected by the developmental state. Basal adenylyl cyclase activity (pmoles cAMP/min x mg protein) increased from 30.9 +/- 5.0, 36.8 +/- 5.0 to 63.9 +/- 5.9 at 1st, 7th and 30th postnatal day, respectively. Isoprenaline (100 microM) enhanced the activity of adenylyl cyclase from day 1, 7-30 from 46.2 +/- 7.0, 79.1 +/- 9.2 to 120.5 7.2, respectively. The effects of forskolin and NaF on adenylyl cyclase activity was found to be not influenced within the first postnatal month. Furthermore, a developmentally controlled expression of cardiac troponin I was observed (6-fold from the first to the 28th postnatal day) whereas the level of phospholamban was found to be age-independent. In conclusion, there is an increase in the efficiency of the beta-adrenergic signal transfer mainly caused by a reduction of the inhibitory G proteins and a dominance of the Gs alpha-linked pathway in the postnatal rat heart. Furthermore the developmentally controlled expression of troponin I might be of functional importance in the cAMP-supported relaxation. Additionally, altered Gq alpha, G(o) alpha and G beta pattern of the developing rat ventricle may play a role in the observed change of alpha-adrenerg-mediated heart contractility as well as in cardiac differentiation and growth processes.

Adenylyl Cyclases↗
PubMedDate not supplied

In-vivo phosphorylation of the cardiac L-type calcium channel beta-subunit in response to catecholamines.

In canine myocardium, the beta-subunit of the L-type Ca2+ channel is phosphorylated by cAMP dependent protein kinase in vitro as well as in vivo (Haase et al. FEBS Lett 335: 217-222, 1993). We have assessed the identity of the beta-subunit as well as its in vivo phosphorylation in representative experimental groups of catecholamine-challenged canine hearts. Adrenergic stimulation by high doses of both noradrenaline and isoprenaline induced rapid (within 20 sec) and nearly complete phosphorylation of the Ca2+ channel beta-subunit. Phosphorylation in vivo was about 4-fold higher as compared to untreated controls. When related to catecholamine-depleted (reserpine-treated) hearts noradrenaline and isoprenaline increased the in vivo phosphorylation of the beta-subunit even 8-fold. This phosphorylation correlated positively with tissue levels of cAMP, endogenous particulated cAMP-dependent protein kinase (PKA) and the rate of contractile force development dP/dtmax. The results imply the involvement of a PKA-mediated phosphorylation of the Ca2+ channel beta-subunit in the adrenergic stimulation of intact canine myocardium.

Animals↗
PubMedDate not supplied

Beta 2-adrenoceptor activation by zinterol causes protein phosphorylation, contractile effects and relaxant effects through a cAMP pathway in human atrium.

Evidence from ventricular preparations of cat, sheep, rat and dog suggests that both beta 1-adrenoceptors (beta 1AR) and beta 2-adrenoceptors (beta 2AR) mediate positive inotropic effects but that only beta 1AR do it through activation of a cAMP pathway. On the other hand, our evidence has shown that both beta 1AR and beta 2AR hasten relaxation of isolated human myocardium consistent with a common cAMP pathway. We have now investigated in the isolated human right atrial appendage, a tissue whose beta-AR comprise around 2/3 of beta 1AR and 1/3 of beta 2AR, whether or not beta 2AR-mediated effects occur via activation of a cAMP pathway. We carried out experiments on atria obtained from patients without advanced heart failure undergoing open heart surgery. To activate beta 2AR, we used the beta 2AR-selective ligand zinterol. Experiments were carried out on paced atrial strips (1 Hz) and tissue homogenates and membrane particles. Zinterol caused positive inotropic and lusitropic (i.e. reduction of t1/2 of relaxation) effects with EC50 values of 3 and 2 nM, respectively. The zinterol-evoked effects were unaffected by the beta 1AR-selective antagonist CGP 20712A (300 nM) but blocked surmountably by the beta 2AR-selective antagonist ICI 118551 (50 nM) which reduced both EC50 values to 1 microM. Zinterol stimulated adenylyl cyclase activity with an EC50 of 30 nM and intrinsic activity of 0.75 with respect to (-)-isoprenaline (600 microM); the effects were resistant to blockade by CGP 20712A (300 nM) but antagonised surmountably by ICI 118551 (50 nM). Zinterol bound to membrane beta AR labelled with (-)-[125I] cyanopindolol with higher affinity for beta 2AR than for beta 1AR; the binding to beta 2AR but not to beta 1AR was reduced by GTP gamma S (10 microM). In the presence of CGP 20712A (300 nM) (-)-isoprenaline (400 microM) (to activate both beta 1AR and beta 2AR maximally) and zinterol (10 microM) increased contractile force 3.4-fold and 2.5-fold respectively and reduced relaxation t1/2 by 32% and 18% respectively. These effects of (-)-isoprenaline and zinterol were associated (5 min incubation) with phosphorylation (pmol P/mg supernatant protein) of troponin I and C-protein to values of 8.4 +/- 2.0 vs 12.4 +/- 2.3 and 10.1 +/- 2.5 vs 8.6 +/- 1.6 respectively. (-)-Isoprenaline and zinterol also caused phosphorylation of phospholamban (1.8 +/- 0.3 vs 0.4 +/- 0.1 pmol P/mg respectively) specifically at serine residues. We conclude that in human atrial myocardium activation of both beta 1AR and beta 2AR leads to cAMP-dependent phosphorylation of proteins involved in augmenting both contractility and relaxation.

Adenosine Triphosphatases↗
PubMedDate not supplied

Activation of beta2-adrenergic receptors hastens relaxation and mediates phosphorylation of phospholamban, troponin I, and C-protein in ventricular myocardium from patients with terminal heart failure.

BACKGROUND: Catecholamines hasten cardiac relaxation through beta-adrenergic receptors, presumably by phosphorylation of several proteins, but it is unknown which receptor subtypes are involved in human ventricle. We assessed the role of beta1- and beta2-adrenergic receptors in phosphorylating proteins implicated in ventricular relaxation. METHODS AND RESULTS: Right ventricular trabeculae, obtained from freshly explanted hearts of patients with dilated cardiomyopathy (n=5) or ischemic cardiomyopathy (n=5), were paced at 60 bpm. After measurement of the contractile and relaxant effects of epinephrine (10 micromol/L) or zinterol (10 micromol/L), mediated through beta2-adrenergic receptors, and of norepinephrine (10 micromol/L), mediated through beta1-adrenergic receptors, tissues were freeze clamped. We assessed phosphorylation of phospholamban, troponin I, and C-protein, as well as specific phosphorylation of phospholamban at serine 16 and threonine 17. Data did not differ between the 2 disease groups and were therefore pooled. Epinephrine, zinterol, and norepinephrine increased contractile force to approximately the same extent, hastened the onset of relaxation by 15+/-3%, 5+/-2%, and 20+/-3%, respectively, and reduced the time to half-relaxation by 26+/-3%, 21+/-3%, and 37+/-3%. These effects of epinephrine, zinterol, and norepinephrine were associated with phosphorylation (pmol phosphate/mg protein) of phospholamban 14+/-3, 12+/-4, and 12+/-3; troponin I 40+/-7, 33+/-7, and 31+/-6; and C-protein 7.2+/-1.9, 9.3+/-1.4, and 7.5+/-2.0. Phosphorylation of phospholamban occurred at both Ser16 and Thr17 residues through both beta1- and beta2-adrenergic receptors. CONCLUSIONS: Norepinephrine and epinephrine hasten human ventricular relaxation and promote phosphorylation of implicated proteins through both beta1- and beta2-adrenergic receptors, thereby potentially improving diastolic function.

Adolescent↗
PubMedDate not supplied

North Carolina's TBI project ACCESS. Assuring coordinated care, education, and support for survivors of pediatric brain injury.

Over the past three years, families, school staff, and healthcare personnel in our state have benefited from an innovative service delivery system designed to demonstrate that we can improve the lives of children with TBI. Project ACCESS has used hospital-based pediatric brain injury Community Transition Coordinators to identify, coordinate care, educate, support, and generally improve the lives of thousands of children with TBI. The project also uncovered a host of barriers that adversely affect the future of many of North Carolina's most vulnerable children. We hope that this article helps delineate the challenges faced by our state's healthcare and educational systems, and contributes to the adoption of a statewide model system of care for children with brain injury.

Adolescent↗