The role of transition radiation in cathodoluminescence imaging and spectroscopy of thin-foils.

There is renewed interest in cathodoluminescence (CL) in the transmission electron microscope, since it can be combined with low energy loss spectroscopy measurements and can also be used to probe defects, such as grain boundaries and dislocations, at high spatial resolution. Transition radiation (TR), which is emitted when the incident electron crosses the vacuum-specimen interface, is however an important artefact that has received very little attention. The importance of TR is demonstrated on a wedge shaped CdTe specimen of varying thickness. For small specimen thicknesses (<250nm) grain boundaries are not visible in the panchromatic CL image. Grain boundary contrast is produced by electron-hole recombination within the foil, and a large fraction of that light is lost to multiple-beam interference, so that thicker specimens are required before the grain boundary signal is above the TR background. This is undesirable for high spatial resolution. Furthermore, the CL spectrum contains additional features due to TR which are not part of the 'bulk' specimen. Strategies to minimise the effects of TR are also discussed.

Reduced cytosolic Ca(2+) loading and improved cardiac function after cardioplegic cold storage of guinea pig isolated hearts.

BACKGROUND: Hypothermia is cardioprotective, but it causes Ca(2+) loading and reduced function on rewarming. The aim was to associate changes in cytosolic Ca(2+) with function in intact hearts before, during, and after cold storage with or without cardioplegia (CP). METHODS AND RESULTS: Guinea pig hearts were initially perfused at 37 degrees C with Krebs-Ringer's (KR) solution (in mmol/L: Ca(2+) 2.5, K(+) 5, Mg(2+) 2.4). One group was perfused with CP solution (Ca(2+) 2.5, K(+) 18, Mg(2+) 7.2) during cooling and storage at 3 degrees C for 4 hours; another was perfused with KR. LV pressure (LVP), dP/dt, O(2) consumption, and cardiac efficiency were monitored. Cytosolic phasic [Ca(2+)] was calculated from indo 1 fluorescence signals obtained at the LV free wall. Cooling with KR increased diastolic and phasic [Ca(2+)], whereas cooling with CP suppressed phasic [Ca(2+)] and reduced the rise in diastolic [Ca(2+)]. Reperfusion with warm KR increased phasic [Ca(2+)] 86% more after CP at 20 minutes and did not increase diastolic [Ca(2+)] at 60 minutes, compared with a 20% increase in phasic [Ca(2+)] after KR. During early and later reperfusion after CP, there was a 126% and 50% better return of LVP than after KR; during later reperfusion, O(2) consumption was 23% higher and cardiac efficiency was 38% higher after CP than after KR. CONCLUSIONS: CP decreases the rise in cardiac diastolic [Ca(2+)] observed during cold storage in KR. Decreased diastolic [Ca(2+)] and increased systolic [Ca(2+)] after CP improves function on reperfusion because of reduced Ca(2+) loading during and immediately after cold CP storage.

Adenosine potentiates coronary flow and inhibits oxygen consumption during isoprenaline infusion in isolated perfused guinea pig hearts.

It has been shown that adenosine, a potent coronary vasodilator, is released during cardiac sympathetic stimulation and that infusion of adenosine reduces the increase in myocardial contractile force elicited by catecholamines. The purpose of our study was: 1) to examine if adenosine also attenuates the rise in O2 consumption (MVO2) induced by infusing isoprenaline; and 2) to determine whether such a fall in MVO2 occurs primarily because of a relative decrease in tissue O2 extraction or a change in coronary flow. We isolated guinea pig hearts, perfused the vasculature at constant pressure and measured coronary flow, inflow and outflow pO2, and isovolumetric left ventricular pressure (PLV) and its derivative (dP/dt). Before, during and after infusing isoprenaline, we infused adenosine at increasing rates; but both drugs were infused at rates which did not maximally increase flow. We observed that adenosine reduced the increases in PLV and +dP/dt due to isoprenaline from 52 to 24% and from 81 to 55%. Moreover, linear regression analysis showed that the rise in MVO2 by isoprenaline was antagonised as a function of adenosine. This relative fall in MVO2 resulted primarily because of a decrease in O2 extraction since coronary flow was enhanced as a function of adenosine. Thus, although adenosine enhances the increase in flow due to isoprenaline overall it attenuates tissue O2 extraction and MVO2. Our study suggests that during sympathetic cardiac stimulation, endogenously released adenosine may not only produce vasodilatation and enhance the delivery of O2, but may also attenuate cardiac muscle work and the extraction of O2 with a net inhibition of MVO2.

Effects of vasodilators and perfusion pressure on coronary flow and simultaneous release of nitric oxide from guinea pig isolated hearts.

OBJECTIVE: The aims were to validate the use of a direct reading NO electrode, to compare the effects of diverse acting drugs on altering coronary flow (CF) and NO release, and to examine the effects of altered perfusion pressure on flow-induced changes in NO concentration [NO] in the hemoglobin free effluent of guinea pig isolated hearts. METHODS: Hearts were isolated and perfused initially at a constant perfusion pressure (55 mmHg) with a modified Krebs-Ringer's solution equilibrated with 97% O2 and 3% CO2 at 37 degrees C. Heart rate, left ventricular pressure, CF, and effluent pH, pCO2, pO2, and NO generated current were monitored continuously on-line. Effluent was sampled for L-citrulline. Percent O2 extraction and O2 consumption were calculated. [NO] was quantitated with a sensitive amperometric sensor (sensitivity > or = 1 nmol/l approximately 3 pA) and a selective gas permeable membrane. RESULTS: The electrode was not sensitive to changes in solution pO2, flow, or pressure. The electrode was sensitive to pCO2 (-0.50 nmol/l/mmHg) and temperature (+24.5 nmol/l/degree C), so coronary effluent pCO2 was measured to compensate for a small decrease in pCO2 that occurred with an increase in coronary flow, and effluent temperature was rigidly controlled. Serotonin, bradykinin, and nitroprusside increased NO release along with CF, whereas nifedipine, butanedione monoxime, zaprinast, and bimakalim comparably increased CF but did not increase [NO] or NO release. Increases in CF (ml/g/min) and NO release (pmol/g/min), respectively, were 5.0 +/- 1 and 100 +/- 17 for 1 mumol/l serotonin, 7.5 +/- 1 and 148 +/- 18 for 100 nmol/l bradykinin, and 7.8 +/- 1 and 173 +/- 28 for 100 mumol/l nitroprusside. The increases in effluent NO by bradykinin were proportional to the increases in L-citrulline. Tetraethylammonium decreased CF, but did not change NO release, indomethacin changed neither CF nor NO release, and NG-nitro-L-arginine methyl ester (L-NAME) reduced CF by 2.6 +/- 1 ml/g/min and NO release by 25 +/- 8 pmol/g/min. An increase of CF of 8.0 +/- 0.3 ml/g/min, produced by increasing perfusion pressure from 25 to 90 mmHg, increased [NO] by 30 +/- 4 nmol/l; L-NAME but did not reduce the pressure-induced increase in CF, but reduced the increase in [NO] to 10 +/- 5 nmol/l. CONCLUSIONS: This study demonstrates in intact hearts real-time release of NO by several vasodilator drugs and by pressure-induced increases in flow (shear stress) and attenuation of these effects by L-NAME.

Protein kinase activities in cell-free extracts of Streptomyces coelicolor A3(2).

Protein kinase activities were detected in cell-free extracts of the B385 derivative of Streptomyces coelicolor A3(2); at least 12 polypeptides, ranging in Mr from 6,000 to 98,000, were detectably phosphorylated, probably as O-monoesters, after incubation with gamma [32P]ATP. The culture stage of the mycelia used for production of the cell-free extracts determined the profile of phosphorylated polypeptides. Phosphoenol pyruvate acted as a potent modulator of the apparent degree of protein kinase activity. In addition Ca2+ ions, verapamil, chlorpromazine and anti-calmodulin antiserum had specific effects on the profile of phosphopolypeptides observed.

Effects of 2,3-butanedione monoxime in isolated hearts: protection during reperfusion after global ischemia.

The cardiac effects of 2,3-butanedione monoxime on electrical and mechanical function, rhythm, oxygen utilization, and coronary flow responsiveness, particularly during severe ischemia and reperfusion, have not been studied. After perfusing hearts at 55 mm Hg, coronary perfusion was interrupted for 30 minutes and was then reestablished at the control perfusion pressure for 40 minutes. Hearts were divided into four groups (n = 10 each) treated with 0, 3, 5, or 10 mmol/L of 2,3-butanedione monoxime added to the perfusate for 10 minutes before and during ischemia and for the first 10 minutes of reperfusion. An additional nonischemic group served as a time control. Variables monitored were heart rate, atrioventricular conduction time, cardiac rhythm, isovolumetric systolic and diastolic left ventricular pressure, maximum rate of left ventricular pressure change, coronary flow, myocardial oxygen consumption, and the ratio of oxygen delivery to myocardial oxygen consumption. Before ischemia, 2,3-butanedione monoxime significantly decreased isovolumetric left ventricular systolic pressure and increased the ratio of oxygen delivery to myocardial oxygen consumption in a dose-dependent manner, with only slight changes in heart rate and atrioventricular time with 10 mmol/L of 2,3-butanedione, monoxime. After 40 minutes of reperfusion, isovolumetric left ventricular systolic pressure recovered to 81 +/- 5% and 83 +/- 2% of the initial control values for the 5 and 10 mmol/L 2,3-butanedione monoxime groups. This was significantly greater than the recovery for the 0 and 3 mmol/L 2,3-butanedione monoxime groups, 59 +/- 3% and 63 +/- 4%, respectively. Similarly, the duration of ventricular fibrillation and of tachycardia was significantly lower, coronary flow reserve was better preserved, and myocardial oxygen consumption was greater with reperfusion in the 5 and 10 mmol/L 2,3-butanedione monoxime groups than in the 0 mmol/L 2,3-butanedione monoxime group. This study shows that relatively low concentrations of 2,3-butanedione monoxime, given before global ischemia and early during reperfusion of isolated hearts, can protect against dysrhythmias and improve return of myocardial and vascular function.

Improvement in functional recovery of the isolated guinea pig heart after hyperkalemic reperfusion with adenosine.

The aim of this study was to examine the effect of initial hyperkalemic reperfusion (HKR), with and without added adenosine, on coronary flow, myocardial function, and endothelium-dependent and endothelium-independent coronary vascular function. Cardioplegic arrest was induced in 40 isolated guinea pig hearts by infusing oxygenated cardioplegic (high in potassium ion) Krebs solution for 5 minutes. Hearts were then stored at room temperature for 3.5 hours. On reperfusion, hearts were divided into four groups of 10 hearts each: control, reperfusion with regular Krebs solution (4.6 mmol/L potassium chloride); base hyperkalemic reperfusion, initial reperfusion with 37 degrees C oxygenated, cardioplegic Krebs solution for 5 minutes; hyperkalemic reperfusion with addition of 1 mmol/L adenosine during HKR; and hyperkalemic reperfusion with addition of 5 mmol/L adenosine. Coronary reserve (adenosine bolus 2 mmol/L) and responses to acetylcholine (1 mumol/L) and nitroprusside (100 mumol/L) were examined before and after ischemia and reperfusion. Flow did not return to preischemic values in any group after reperfusion. Adenosine treatment during initial reperfusion increased coronary flow (percentage of baseline +/- standard error of the mean) from 57% +/- 4% in control and 45% +/- 3% in hearts with hyperkalemic reperfusion to 79% +/- 3% and 83% +/- 5% in hearts with hyperkalemic reperfusion also treated with, respectively, 1 mmol/L adenosine and 5 mmol/L adenosine (p < 0.05). At 30 and 60 minutes of reperfusion, however, flow remained elevated only in the group treated with 5 mmol/L adenosine. Coronary reserve and responses to acetylcholine and nitroprusside were equivalently depressed in all groups after reperfusion. Recovery of left ventricular systolic and diastolic function was improved in all groups after hyperkalemic reperfusion (54% +/- 4% of preischemic value) compared with control (39% +/- 3%), and recovery was further enhanced in the group treated with 5 mmol/L adenosine (60% +/- 4%). In this ex vivo model, hyperkalemic reperfusion improved myocardial function after cardioplegic arrest and the addition of 5 mmol/L adenosine improved coronary flow. Adenosine may counteract the potassium chloride-induced vasoconstriction that occurs during hyperkalemic reperfusion and may thus improve coronary flow and myocardial function. Postischemic depression of endothelium-dependent or endothelium-independent vascular functions, however, was not alleviated by hyperkalemic reperfusion with or without adenosine.

Effects of hypoxia on adult and neonatal pacemaker rates.

Fetal bradycardia during parturition may result both from autonomic reflex effects and from the direct effect of hypoxia on the myocardium. To compare the relative sensitivities of neonatal and adult sinoatrial nodes to hypoxia, action potentials were recorded simultaneously from isolated neonatal and adult sinoatrial nodal tissues of the guinea pig with intracellular microelectrodes. Action potential rates were measured during normoxia and hypoxia, with and without acidosis, glucose, and epinephrine. Control (PO2 greater than 450 torr) intrinsic pacemaker activity was higher in the neonate than in the adult (296 versus 222 beats per minute). Epinephrine maximally increased rates to similar levels in the two age groups. Hypoxia (PO2 equals 33 torr) markedly lowered adult (44%) and neonatal (35%) rates, but the fall in rates was similar. The addition of acidosis or the removal of glucose during hypoxia produced a greater fall of pacemaker rates in the neonates compared with the adults. The addition of epinephrine during hypoxia caused adult rates to increase to control normoxic levels, but neonatal rates remained significantly depressed below control levels. The results suggest that the neonatal pacemaker node is no better protected against bradycardia during hypoxia alone than is the adult node, but that the neonatal node is more susceptible to bradycardia induced by hypoxia with acidosis or removal of glucose. The hypoxic neonatal node, moreover, responds with a lesser increase in pacemaker rate during epinephrine stimulation than does the adult node.

Initial reperfusion with 2,3 butanedione monoxime is better than hyperkalemic reperfusion after cardioplegic arrest in isolated guinea pig hearts.

OBJECTIVE: Initial warm cardioplegic reperfusion is widely used to ameliorate cardiac reperfusion damage after cardioplegic arrest. However, undesired effects of the high potassium concentration of the cardioplegic perfusate may limit the beneficial effect of this treatment. Contraction uncoupling by a negative inotropic and vasodilating agent such as 2,3-butanedione monoxime (BDM) may be superior to warm cardioplegic reperfusion in reducing reperfusion damage. Thus, initial reperfusion with BDM was compared with hyperkalemic reperfusion (HKR) after global ischemia of Langendorff-perfused guinea pig hearts. METHODS: Cardiac arrest was induced in 16 hearts using hyperkalemic Krebs' solution and hearts were stored unperfused at 37 degrees C for 40 min. Two groups were studied: HKR, initial reperfusion with 37 degrees C oxygenated hyperkalemic Krebs' for 5 min, and BDM, addition of 20 mM BDM to normokalemic Krebs' for 5 min. RESULTS: BDM increased reactive coronary reflow (128 +/- 8%; all data mean +/- SEM of baseline) much more than HKR treatment (65 +/- 5%). O2 consumption was reduced more by HKR (28 +/- 1%) than by BDM (42 +/- 4%), but the O2 supply/consumption ratio was higher with BDM. During perfusion with normal Krebs' solution, flow stabilized at about 75% of baseline in both groups. Post-ischemic responses to adenosine, serotonin, and nitroprusside were depressed to a similar degree in both two groups. Recovery of left ventricular developed pressure was better in BDM (69 +/- 2%) than in HKR (61 +/- 3%)-treated hearts. Reperfusion dysrhythmias were markedly reduced after BDM reperfusion. CONCLUSIONS: These data indicate that treatment in the initial 5-min reperfusion period with BDM is more effective than hyperkalemic reperfusion in reducing reperfusion damage.

Comparison of hyperkalemic cardioplegia with altered [CaCl2] and [MgCl2] on [Ca2+]i transients and function after warm global ischemia in isolated hearts.

AIM: [MgCl(2)] and [CaCl(2)] may modify the cardioprotective effects of hyperkalemic cardioplegia (CP). We changed [MgCl(2)] and [CaCl(2)] in a CP solution to examine their effects on [Ca(2+)]i transients and cardiac function before and after global normothermic ischemia. METHODS: After stabilization and loading of indo 1-AM in Kreb's solution (KR), each heart was perfused with either KR or 1 of 4 CP solutions before 37 degrees C, 30 min ischemia followed by reperfusion with KR. The KR solution contained, in mM, 4.5 KCl, 2.4 MgCl(2) and 2.5 CaCl(2); the CP solutions had in addition to 18 KCl: CP 1 (control CP): 2.4 MgCl(2), 2.5 CaCl(2); CP 2: 7.2 MgCl(2), 2.5 CaCl(2); CP 3, 7.2 MgCl(2), 1.25 CaCl(2); CP 4: 2.4 MgCl(2), 1.25 CaCl(2). RESULTS: In the KR group [Ca(2+)]i markedly increased on early reperfusion while functional return (LVP, dLVP/dt((max and min))) was much reduced; each CP group led to reduced [Ca(2+)]i loading and improved function. The rates of cytosolic Ca(2+) fluxes (d[Ca(2+)]/dt(max) and d[Ca(2+)]/dt(min)) increased significantly compared to baseline in the KR group, but were mostly suppressed in the CP groups, and d[Ca(2+)]/dt(min) was lower after CP 4 compared to CP 1 on reperfusion. At 60 min reperfusion, LVP area to [Ca(2+)] area and cardiac efficiency to phasic [Ca(2+)] relationships were shifted after KR, but not after CP 1-4. With similar functional recovery, [Ca(2+)] transient and [Ca(2+)] area were significantly lower after CP 4 than after CP 1. CONCLUSION: Increasing [MgCl(2)] (CP 2 and 3) did not improve cardiac function or reduce Ca(2+) transients on reperfusion better than the other CP groups, but reducing [CaCl(2)] (CP 3 and 4) was more effective in reducing [Ca(2+)] transients on reperfusion after global ischemia.

Attenuation of hemodynamic responses to rapid sequence induction and intubation in healthy patients with a single bolus of esmolol.

The effectiveness of a single preinduction intravenous (IV) bolus of esmolol in blunting hemodynamic responses to rapid sequence induction and tracheal intubation was evaluated. In a randomized double-blind study, 32 ASA I and II healthy patients scheduled for surgery were monitored with electrocardiography (EKG) lead V5, arterial cannulation, and impedance cardiography. After preoxygenation and a priming dose of vecuronium (0.01 mg/kg), patients received either saline (n = 12), esmolol 100 mg (n = 10), or esmolol 200 mg (n = 10) as an IV bolus (20 ml volume). This procedure was immediately followed by a 5 ml IV saline flush, cricoid pressure, thiopental sodium 5 mg/kg, and succinylcholine 1.5 mg/kg. Patients receiving 200 mg of esmolol had a 50% reduction in the usual tachycardia associated with induction and a greater decline in systolic blood pressure (SP) (by 50%) prior to intubation as compared with the placebo group (p less than 0.05). The increase in diastolic blood pressure (DP) and the reduction in stroke volume (SV) produced by induction and intubation were similar in all the groups. Plasma norepinephrine levels at 1.5 minutes after intubation increased in the esmolol groups about 130% above that measured in the placebo group. This finding was associated with a more gradual return of peripheral resistance to baseline following tracheal intubation. However, both doses of esmolol effectively attenuated heart rate (HR), SP, and rate pressure product (RPP) increases (p less than 0.05 vs placebo) produced by laryngoscopy and tracheal intubation.

Partial attenuation of hemodynamic responses to rapid sequence induction and intubation with labetalol.

The effectiveness of labetalol (a combination nonselective beta and alpha-1-adrenergic receptor antagonist) in modifying hemodynamic responses associated with rapid sequence induction and tracheal intubation was evaluated. In a double-blind study, 24 ASA physical status I or II male patients scheduled for elective surgery were given either IV labetalol, 0.25 mg/kg (n = 8) or 0.75 mg/kg (n = 8), or a saline placebo (n = 8). Five minutes later, patients were given oxygen by mask and IV vecuronium, 0.01 mg/kg. Ten minutes after giving labetalol or placebo, cricoid pressure was applied and anesthesia was induced with IV sodium thiopental (4 mg/kg) and succinylcholine (1.5 mg/kg) 1 minute prior to intubation. The mean duration of laryngoscopy was 17 +/- 3 seconds. Prior to induction, the 0.25 mg/kg and 0.75 mg/kg doses of labetalol significantly (p less than 0.05) reduced mean arterial pressure by 4.4 +/- 1.9 and by 8.6 +/- 2.0 mmHg, respectively, but did not significantly alter heart rate or cardiac output. The 0.75 mg/kg dose of labetalol also significantly (p less than 0.05) decreased total peripheral resistance by 10.1 +/- 3.0%. Within 30 seconds after intubation, patients in all three groups exhibited increases in heart rate, mean arterial pressure, total peripheral resistance, and rate pressure product and a decrease in stroke volume. However, patients in the 0.25 and 0.75 mg/kg labetalol groups, compared to those in the placebo group, had significantly lower increases in peak heart rate (33 +/- 2 and 27 +/- 3 vs. 44 +/- 7 beats/minute), peak mean arterial pressure (38 +/- 6 and 38 +/- 7 vs. 58 +/- 7 mmHg), and peak rate pressure product (7,726 +/- 260 and 7,215 +/- 300 vs. 14,023 +/- 250 units). The results show that these doses of labetalol significantly blunt, but do not completely block, autonomic responses to rapid sequence induction and intubation.

Mitochondrial inner membrane electrophysiology assessed by rhodamine-123 transport and fluorescence.

Rhodamine-123 is widely used to make dynamic measurements of mitochondrial membrane potential both in vitro and in situ. Yet data interpretation is difficult due to a lack of quantitative understanding of how membrane potential and measured fluorescence are related. To develop such understanding, a model for dye transport across the mitochondrial inner membrane and partition into the membrane was developed. The model accounts for experimentally measured dye self-quenching and was integrated into a model of mitochondrial electrophysiology to estimate transients in mitochondrial membrane potential from kinetic fluorescence measurements. Our analysis indicates that (i) R123 fluorescence peaks at concentrations near 50 microM due to self-quenching; (ii) measured fluorescence intensity and membrane potential are related by a non-linear calibration curve sensitive to certain experimental details, including total concentration of dye and mitochondria in suspensions; and (iii) the time courses of membrane potential and electron transport fluxes following a perturbation (i.e. addition of ADP) significantly differ from observed transients in fluorescence intensity. These findings are consistent with the model predictions that mitochondria display a characteristic time of response to changes in substrate concentration of less than 0.1 s, corresponding to the time scale over which the rate of ATP synthesis changes to meet changes in ADP concentration.

Heart bioassay of effluent of isolated, perfused guinea pig hearts to examine the role of metabolites regulating coronary flow during hypoxia.

The concentrations of adenosine and other metabolic factors are known to be altered in the effluent of hypoxic hearts, but the relative contribution of these factors in elevating coronary flow has not been clarified. Langendorff prepared guinea pig hearts were perfused at constant pressure and were made mildly hypoxic so that flow increased but oxygen consumption remained unchanged. When the effluent of these hearts was reoxygenated and pH corrected and directed to perfuse similarly prepared recipient (bioassay) hearts, flow remained unchanged in recipient hearts. However, when donor hearts were made severely hypoxic so that oxygen consumption decreased, and recipient hearts were perfused at constant flow, the PO2, pH corrected effluent produced a large vasodilation in recipient hearts. This response was greatly attenuated in the presence of excess adenosine deaminase but completely abolished by theophylline. Thus the apparent loss of adenine compounds into the effluent may account for vasodilation during severe hypoxia, but not during mild hypoxia, if effluent levels of these compounds truly reflect perivascular levels.