Ploidy-stratified single cardiomyocyte transcriptomics map Zinc Finger E-Box Binding Homeobox 1 to underly cardiomyocyte proliferation before birth

Whereas cardiomyocytes (CMs) in the fetal heart divide, postnatal CMs fail to undergo karyokinesis and/or cytokinesis and therefore become polyploid or binucleated, a key process in terminal CM differentiation. This switch from a diploid proliferative CM to a terminally differentiated polyploid CM remains an enigma and seems an obstacle for heart regeneration. Here, we set out to identify the transcriptional landscape of CMs around birth using single cell RNA sequencing (scRNA-seq) to predict transcription factors (TFs) involved in CM proliferation and terminal differentiation. To this end, we established an approach combining fluorescence activated cell sorting (FACS) with scRNA-seq of fixed CMs from developing (E16.5, P1, and P5) mouse hearts, and generated high-resolution single-cell transcriptomic maps of in vivo diploid and tetraploid CMs, increasing the CM resolution. We identified TF-networks regulating the G2/M phases of developing CMs around birth. ZEB1 (Zinc Finger E-Box Binding Homeobox 1), a hereto unknown TF in CM cell cycling, was found to regulate the highest number of cell cycle genes in cycling CMs at E16.5 but was downregulated around birth. CM ZEB1-knockdown reduced proliferation of E16.5 CMs, while ZEB1 overexpression at P0 after birth resulted in CM endoreplication. These data thus provide a ploidy stratified transcriptomic map of developing CMs and bring new insight to CM proliferation and endoreplication identifying ZEB1 as a key player in these processes.

Apex Resection in Zebrafish (Danio rerio) as a Model of Heart Regeneration: A Video-Assisted Guide

Ischemic heart disease is one of the leading causes of deaths worldwide. A major hindrance to resolving this challenge lies in the mammalian hearts inability to regenerate after injury. In contrast, zebrafish retain a regenerative capacity of the heart throughout their lifetimes. Apex resection (AR) is a popular zebrafish model for studying heart regeneration, and entails resecting 10-20% of the heart in the apex region, whereafter the regeneration process is monitored until the heart is fully regenerated within 60 days. Despite this popularity, video tutorials describing this technique in detail are lacking. In this paper we visualize and describe the entire AR procedure including anaesthesia, surgery, and recovery. In addition, we show that the concentration and duration of anaesthesia are important parameters to consider, to balance sufficient levels of sedation and minimizing mortality. Moreover, we provide examples of how zebrafish heart regeneration can be assessed both in 2D (immunohistochemistry of heart sections) and 3D (analyses of whole, tissue cleared hearts using multiphoton imaging). In summary, this paper aims to aid beginners in establishing and conducting the AR model in their laboratory, but also to spur further interest in improving the model and its evaluation.

Design and evaluation of a handheld impedance plethysmograph for measuring heart rate variability

Heart rate variability (HRV) analysis from 10s ECGs has been shown to be reliable. However, the short examination time warrants a user-friendly system that can be used for ad-hoc examinations without normal preparation, unlike ECG. A handheld device has been developed that can measure ultra-short HRV from impedance plethysmographic recordings of the pulse wave in distal superficial arteries. The prototype device was made user-friendly through a compact, pen-like design and the use of integrated metal electrodes that were especially designed for dry operation. The main signal processing was performed by a digital signal processor, where the discrete heart beats were detected using a correlation algorithm that could adapt to individual pulse wave shapes to account for biological variation. The novel device was evaluated in 20 mainly young volunteers, using 10 s time-correlated ECG recordings as the reference method. Agreement between the two methods in measuring heart rate and root mean square of successive differences in the heart beat interval (RMSSD) was analysed using correlation coefficients (Pearson's R2), mean differences with 95% confidence intervals and 95% limits of agreement, and Bland-Altman plots. The correlation between the two methods was R2 = 1.00 and R2 = 0.99 when heart rate and RMSSD were measured, respectively. The Bland-Altman plots showed suitable agreement between the novel device and standard 10 s ECGs, which was substantiated by 95% limits of agreement of the difference of +/- 0.1 beats min(-1) and approximately +/- 10 ms for heart rate and RMSSD, respectively. Therefore the evaluation showed no significant systematic error of the novel device compared with ECG.

Rewarming from accidental hypothermia by extracorporeal circulation. A retrospective study

OBJECTIVE

Twenty-six patients with accidental hypothermia combined with circulatory arrest or severe circulatory failure were rewarmed to normothermia by use of extracorporeal circulation (ECC). The aim of the present study was to evaluate our results.

PATIENTS AND METHODS

The treatment of six female and 20 male patients (median age: 26.7 years; range 1.9--76.3 years) rewarmed in the period 1987--2000 was evaluated retrospectively. Hypothermia was related to immersion/submersion in cold water (n=17), avalanche (n=1) or prolonged exposure to cold surroundings (n=8). Prior to admission, the trachea was intubated and cardiopulmonary resuscitation (CPR) initiated in all patients with cardiorespiratory arrest (n=22), whereas in those with respiration/circulation (n=4) only oxygen therapy via a face mask was given.

RESULTS

Nineteen of the 26 patients were weaned off ECC whereas seven died because of refractory respiratory and/or cardiac failure. Eight of the 19 successfully weaned patients were discharged from hospital after a median of 10 days. One patient died 3 days after circulatory arrest (complete atrioventricular block) resulting in severe cerebral injury. The remaining ten patients died following 1--2 days due to severe hypoxic brain injury (n=5), cerebral bleeding (n=1) or irreversible cardiopulmonary insufficiency (n=4). Based on the reports from the site of accident, two groups of patients were identified: the asphyxia group (n=15) (submersions (n=14); avalanche accident (n=1)) and the non-asphyxia group (n=11) (patients immersed or exposed to cold environment). Seven intact survivors discharged from hospital belonged to the non-asphyxia group whereas one with a severe neurological deficit was identified within the asphyxia group.

CONCLUSION

Patients with non-asphyxiated deep accidental hypothermia have a reasonable prognosis and should be rewarmed before further therapeutic decisions are made. In contrast, drowned patients with secondary hypothermia have a very poor prognosis. The treatment protocol under such conditions should be the subject for further discussion.

[Rewarming of patients with accidental hypothermia with the help of heart-lung machine]

BACKGROUND

Different techniques have been used for treatment of victims with accidental hypothermia. We have used cardiopulmonary bypass (CPB) for rewarming hypothermic patients with circulatory failure or cardiac arrest. This report summarises our experiences with this patient group.

MATERIAL AND METHODS

23 patients, submersions (n = 15), avalanche (n = 1) and primary hypothermia (immersion/air cooling) (n = 7), were rewarmed using extracorporeal circulation with standard equipment for open-heart surgery.

RESULTS

On a clinical basis, two patient populations could be identified; one group for whom asphyxia was probably present prior to and during cooling, and another group for whom asphyxia was unlikely. In the first group, one of 13 patients survived compared to the latter group where six out of ten survived. A search for laboratory and other variables that with certainty could contribute to the prediction of prognosis was unsuccessful.

INTERPRETATION

Due to lack of safe prognostic predictors, all accidental hypothermic victims with circulatory failure should be rewarmed by cardiopulmonary bypass before further therapeutic decisions are made.

The reforming states group and the promotion of federalism

Since 1991, leaders in health policy from the legislative and executive branches of state government have come together, with financial support and staff collaboration from the Milbank Memorial Fund, to share their experiences and to work on practical solutions to pressing health care problems. What began with a handful of states at the forefront of health reform is now the Reforming States Group (RSG), a bipartisan, voluntary association that includes leaders from over 40 states. This article describes the origins, history, and future prospects of the RSG.

Surgical treatment of spontaneous pneumothorax by wedge resection without pleurodesis or pleurectomy

OBJECTIVE

Evaluation of wedge resection of the lung without pleurodesis or pleurectomy as a method of surgical treatment for spontaneous pneumothorax in terms of complications, recurrence rate and postoperative complaints.

METHODS

Retrospective study of 132 operations for spontaneous pneumothorax in 120 patients (84 men and 36 women: mean age 34 years, range 14-77) performed between 1974 and 1993. The mean observation time was 84 months (range 6-229) and a 100% follow-up rate of all survivors (97%) was achieved.

RESULTS

The indications for surgery were recurrent pneumothorax (52%), persisting air leak during first episode (45%), or hemothorax (3%). Perioperative findings were single bullous disease (86%), 2-3 bullae (6%), diffuse bullous disease (5%) and no bullous disease in 3% of the cases. The overall complication rate was 16% (30-day mortality 1%, reoperation for postoperative bleeding 2%, bronchopneumonia 8%, new pneumothorax during hospital stay 5%). The late recurrence rate (operated lung) was 5%. All recurrences were successfully treated by drainage (n = 3), exsufflation (n = 1) or observation only (n = 3). Reoperation was not necessary. Thirty-seven percent of the patients had postoperative complaints which they associated with the operation.

CONCLUSION

Lung resection without pleurodesis or pleurectomy is a simple, safe and effective method of the surgical treatment of spontaneous pneumothorax in terms of complications and recurrence rate in patients with limited bullous disease.

[Antibiotic prevention and occurrence of wound infections in heart surgery and vascular surgery]

Post-operative wound infections are serious complications in cardiovascular surgery. In order to examine the routines for prophylactic antibiotics and frequency of wound infections, questionnaires were sent to heart and vascular surgery units in Norway. In heart surgery, the sternal wound infection rate registered during stay in hospital varied between 0-1.2%. Seven clinics used cephalothin prophylaxis and one cloxacillin and penicillin. One clinic added vancomycin in the case of valvular surgery. The duration of prophylaxis varied from six hours to four days. In vascular surgery, superficial wound infection rates of 1.5-4.0%, and deep infection rates of 0.8-2.0%, were reported. Seven clinics used cephalothin and three cefuroxime as prophylaxis. The duration of prophylaxis varied from one single dose to several days. In conclusion, the reported infection rates indicate that the antibiotic prophylaxis regimens used help to provide satisfactory protection against wound infections.

Dilation of the internal mammary artery by external papaverine application to the pedicle--an improved method

Spasm of the internal mammary artery (IMA) during coronary bypass grafting may cause inadequate graft flow and makes accurate placement of sutures difficult. In addition, IMAs with poor intraoperative flow rates are more likely to occlude. In this study three methods for spasm prevention were compared in 51 patients undergoing coronary bypass surgery. In group 1, IMA pedicles were covered with a sponge soaked with papaverine solution (0.8 mg/ml of papaverine in 0.9% saline) and left intact distally, thus allowing continuous blood flow until used for bypass. In group 2, the IMAs were divided and clamped distally and the pedicle tucked into a papaverine-soaked sponge. In group 3, the IMAs were also divided distally, clamped, and placed under the upper sternum submerged in papaverine solution (0.8 mg/ml) inside a surgical glove. Free flow from the IMA was higher in group 3 than in groups 1 and 2 (60 ml/min vs. 44 and 30, respectively, P < 0.03). Morphometric measurements disclosed a larger luminal area and less folding of the internal elastic lamina in group 3 compared with groups 1 and 2 (0.73 mm2 vs 0.33 and 0.37, respectively, P < 0.03). Submersion in papaverine solution thus provides better procurement of IMA grafts than storage of the pedicle in a papaverine-soaked sponge.

[Deep accidental hypothermia with asystole. A successful treatment with heart-lung machine after prolonged cardiopulmonary resuscitation]

Extracorporeal circulation can be utilized successfully to rewarm accidental hypothermia victims. This paper describes a 51 year-old man who had been immersed in cold sea water for about 45 minutes. At the time of rescue his ECG was isoelectric. The core temperature was 27 degrees C. Cardiopulmonary resuscitation was performed for 190 minutes before extracorporeal circulation was established. Without active surface rewarming the temperature had dropped to 24 degrees C. Biventricular heart failure became evident during rewarming. Sternotomy and pericardiotomy were carried out to exclude cardiac tamponade, which was not found. After two hours of reperfusion the patient could be weaned from bypass supported by high-dose vasopressor infusion. He was extubated the following day. He was discharged after 12 days without any signs of permanent damage to organs.

Accidental hypothermia with cardiac arrest: complete recovery after prolonged resuscitation and rewarming by extracorporeal circulation

A 51-year-old male remained immersed in sea water (6 degrees C) for 40 min. Brought ashore, the ECG showed asystole. Advanced life support was immediately commenced. On arrival in hospital his rectal temperature was 27 degrees C, but continued to fall to 24 degrees C. The ECG remained isoelectric. Cardiopulmonary resuscitation was continued until extracorporeal circulation was established 190 min after rescue. Upon rewarming ventricular fibrillation occurred which was converted to sinus rhythm with a bolus of lignocaine followed by D.C. conversion at 31.5 degrees C. When rewarming was complete after 60 min, signs of severe heart failure became evident. Sternotomy and pericardiotomy were performed to exclude cardiac tamponade. After 60 min of re-perfusion the patient was be weaned from bypass supported by a high-dose vasopressor infusion and nitroglycerine. He was discharged after 13 days with no evidence of any permanent organ damage. Given the advantage of providing circulatory support, extracorporeal circulation may be useful when rewarming hypothermic victims with cardiac arrest.

Intensive home health care in the United States. Financing as technology

This paper assesses the impact of mechanisms for financing intensive home health care services in the United States on their utilization. As lengths of stay have decreased in response to prospective payment methods for hospitals, demand has increased for intensive and complex services provided to patients in the home. Third-party payers, however, are willing to satisfy only some of this potential demand that their reimbursement policies have generated. It is the policies of payers rather than the safety and effectiveness of devices and procedures that are the major constraints on the expansion of intensive home health care. We describe the effects of these policies on who receives intensive home health care services, who provides them, what services are provided, how their quality is monitored, and what they cost.

Is reduced cardiac performance the only mechanism for myocardial infarct size reduction during beta adrenergic blockade?

Equal reductions in heart rate (44 beats X min-1) were obtained in cats by treatment with either the beta blocking agent timolol or alinidine, an agent claimed to cause bradycardia without interfering with beta adrenoceptor function. Infarct size was measured by staining with triphenyltetrazolium-chloride after 5 h of coronary occlusion and related to the area of hypoperfused myocardium as measured by autoradiography. Regional myocardial blood flow was measured by 15 micron radiolabelled microspheres. Compared with the control cats, in whom 87.4 (SEM 2.2)% of hypoperfused myocardium developed into necrosis, timolol reduced infarct size to 65.8 (SEM 2.6)% (p less than 0.001) and alinidine to 76.2 (SEM 3.1)% (p less than 0.01) of the hypoperfused area. Timolol reduced infarct size more than did alinidine (p less than 0.01). Necrosis was more extensive in the endocardium than in the epicardium in all groups. In the subendocardium timolol and alinidine reduced infarct size to the same extent, whereas timolol reduced infarct size more than alinidine in the subepicardium. Although heart rate proved to be the dominant haemodynamic predictor of infarct size, this study indicates that mechanisms other than reduced oxygen demand associated with bradycardia and cardiodepression are operating in the ischaemic myocardium during beta adrenergic blockade.

Does infarct size influence loss of embolised 15-micrometer microspheres from ischaemic myocardium?

The relationship between myocardial infarct size and loss of 15-micron microspheres from ischaemic tissue was investigated in anaesthetized cats. Radioactive microspheres were injected in the left atrium before and 5 h after left anterior descending coronary artery occlusion. Left ventricular hypoperfused zone (HZ) averaged 36.6% and infarct size (IS) 31.6%. Thus, 86% of HZ evolved into necrosis. Preocclusion blood flow was lower in ischaemic (1.62 ml/min per g) compared with non-ischaemic myocardium (2.09, p = 0.002), indicating 22% microsphere loss. In ischaemic subendocardium, oedema (3.7%) could account for the apparent loss. In ischaemic subepicardium, oedema was less pronounced and 18% physical sphere loss occurred. Subepicardial loss increased in proportion to IS and IS/HZ ratio (r2 = 0.71; p less than 0.005). Non-entrapment of 15-micron spheres in coronary circulation averaged 0.6%, and preocclusion spheres appeared in coronary sinus blood throughout the ischaemic period. In systemic circulation, non-entrapment during injection of preocclusion spheres was 7.8%, but only 1.8% 5 h later. Release of postocclusion spheres took place during KCl injection. Thus, myocardial ischaemia is associated with alterations in microvascular function allowing release of entrapped 15-micron spheres. Also, the magnitude of microsphere loss per gram tissue is related to infarct size.

Myocardial blood flow conditions at re-perfusion following acute ischaemia

The purpose of this study was to investigate the effect of re-perfusion upon distribution of radioactive microspheres in ischaemic myocardium. Ten anaesthetized cats were given 15-micron microspheres prior to left anterior coronary artery occlusion, at 1 h of occlusion, and after 1 h of subsequent re-perfusion. Pre-occlusion blood flow estimates were lower in tissue which had been ischaemic compared with nonischaemic regions in the same heart (1.44 versus 1.87 ml X min-1 X g-1, p less than 0.001), corresponding to 23% apparent loss. Loss also occurred in ischaemic right ventricular tissue (32%). In left ventricular ischaemic endocardium, apparent loss was due to development of oedema. Oedema was also significant in epicardial ischaemic tissue. Correction for oedema eliminated two-fifths of the loss, while three-fifths was due to physical loss. Oedema increased linearly with the level of re-perfusion. During re-perfusion, myocardial blood flow in previously ischaemic tissue was inhomogeneously distributed and, on average, 28% lower than in non-ischaemic myocardium. The 15-micron spheres appeared to pass through capillaries in the ischaemic subepicardium, but this process was not enhanced by reperfusion.

Measurement of local blood flow in acute myocardial infarction: loss of 15-micron microspheres during the first hour

Distribution of radiolabelled microspheres is widely utilized for determination of regional blood flow in experimental myocardial infarction studies. The purpose of this investigation was evaluation of the microsphere method during 1 h of regional ischaemia. Special attention was focused upon loss of preocclusion microspheres from ischaemic myocardium; mechanisms for loss and blood flow distribution in non-ischaemic left ventricle. Microspheres (15 micron) were injected into the left atrium in nine pentobarbital anaesthetized cats prior to coronary artery occlusion and again after 1 h of occlusion. Preocclusion blood flow estimates were lower in ischaemic compared with non-ischaemic myocardium (1.36 vs. 1.62 cm3 X min-1 X g-1, P = 0.002), corresponding to 16% apparent loss. In endocardial ischaemic tissue, development of oedema could account for the loss. In epicardial ischaemic tissue, oedema was not present and loss was therefore due to migration of microspheres. Epicardial loss increased in proportion to restoration of left ventricular contractility. There was no evidence for significant microsphere loss through lymphatic pathways. In non-ischaemic left ventricular tissue, myocardial blood flow was evenly distributed from apex to base, and also between endocardial and epicardial layers. This study quantitates an important limitation to measurements of local blood flow in ischaemic myocardium by radiolabelled microspheres.

Stability of 8-, 15-, and 26-micron microspheres entrapped in feline myocardium

The stability of 8-, 15-, and 26-micron radioactive microspheres entrapped in ischemic and nonischemic myocardium and possible mechanisms for microsphere loss were investigated. Anesthetized cats were given microspheres prior to left anterior descending coronary artery occlusion (or sham operation) and 8 h later. Eight-micron microspheres, compared with 15-micron spheres, underestimated preocclusion myocardial blood flow in ischemic and nonischemic tissue by 30%. With 26-micron spheres, endocardial-to-epicardial blood flow ratio was 1.28. In nonischemic tissue, no loss of 15- and 26-micron microspheres occurred during 8 h. In ischemic myocardium, however, 15% apparent loss of 15- and 26-micron preocclusion spheres took place. In endocardial ischemic tissue, edema could account for 50% of the 15-micron microsphere loss and almost completely for loss of 26-micron spheres. In epicardial ischemic tissue, microsphere loss was not influenced by edema. We found no hemodynamic variable that could predict the magnitude of microsphere loss. Only weak evidence for migration of 15- and 26-micron microspheres through lymphatic pathways was found. Most likely the spheres migrated through venous pathways to embolize in the lungs. We conclude that 15-micron microspheres provide the most reliable tissue blood flow estimates in normal myocardium, but even for these spheres significant loss occurs during 8 h of ischemia.

Effects of timolol on blood flow distribution in the feline myocardium with acute regional ischaemia during controlled haemodynamic conditions

The beta-adrenergic blocking agent timolol was given to cats with acute coronary artery ligation under controlled haemodynamic conditions. Regional myocardial tissue flow was measured by the distribution of labelled microspheres. Timolol reduced cardiac contractility and left ventricular end-diastolic pressure rose, whereas heart rate and ventricular systolic pressure were kept constant by atrial pacing and aortic clamping. The systolic period increased following timolol administration under these conditions. Myocardial blood flow remained unchanged in central ischaemic and border areas, whereas flow increased both endocardially and epicardially in normally perfused area following timolol administration. Without pacing there was a significant flow reduction in the epicardium of the normally perfused area, compared with the situation where heart rate was constant. Under controlled haemodynamic conditions, therefore, timolol appears to improve coronary perfusion in normal myocardium, whereas blood flow to ischaemic myocardium remains essentially unchanged.

Effect of timolol on blood flow distribution in the myocardium during acute regional ischaemia in cats

The beta-adrenergic blocking agent timolol was given to cats with acute coronary artery ligation. Regional myocardial tissue flow was measured by the distribution of 15 micrometers labelled microspheres. Timolol reduced heart rate, cardiac contractility and left ventricular systolic pressure, but end-diastolic pressure rose. Ischaemic tissue blood flow remained unchanged following timolol, thus improving the marked imbalance between oxygen demands and delivery. In normal areas of the myocardial tissue flow was reduced, indicating the beta 2-adrenergic blocking effect of timolol. This was also the case for the border area between ischaemic and non-ischaemic tissue, but significantly less flow reduction was found on the endocardial side than on the epicardial side in the border area. Except for this latter observation, timolol does not appear to improve coronary perfusion. The present study, therefore, indicates that beneficial effects of timolol on ischaemic myocardium are mainly related to a reduction of myocardial oxygen demand.

Pulmonary circulation and loss of microspheres from the lung following acute pulmonary venous occlusion

The pulmonary vein from right upper lobe was ligated in 15 rats while 15 others served as controls. Prior to occlusion, 15 mum microspheres were injected into the superior caval vein. Another population of 15 mum microspheres was similarly given 1 min, 10 min or 30 min after ligation. All rats were killed 5 min after the second microsphere injection. The weight of the ligated lobe was 63% higher than that of the controls. This was probably due to acute vascular congestion since no significant oedema developed. Increased weight caused a reduction in the number of preocclusion microspheres per gram of tissue in the ligated lobe. In addition a gradual loss of preocclusion microspheres took place following pulmonary venous ligation. After 35 min of ligation, 30% of the preocclusion spheres had disappeared from the ligated lobe. Postocclusion flow through the pulmonary artery into right upper lobe was estimated by microspheres from the second injection, and averaged 5% of normal flow. Following acute venous occlusion, a rapid dilatation of the bronchopulmonary communicating system probably takes place. By reversal of the flow in this system, blood and microspheres can be drained into the bronchial venous circulation. In spite of methodological problems caused by acute congestion and loss of microspheres after pulmonary venous occlusion, we consider the microsphere method to be useful for further studies of collateral lung circulation.

Migration of 15 micron microspheres from infarcted myocardium

The fate of 15 micrometers microspheres in ischaemic myocardial tissue was investigated. The spheres were delivered to the left atrium before acute coronary artery ligation. 10 h later the myocardium was examined for its contents of preocclusion spheres, as well as spheres delivered immediately before sacrifice. The ischaemic tissue contained 11 to 60% less preocclusion spheres, compared with nonischaemic tissue in the same hearts. On average, 26% of preocclusion spheres were lost during the 10 h period. Negligible amounts of the lost spheres could be retrieved from cardiac lymph nodes in the mediastinum. Most likely, the spheres migrated through venous pathways; a substantial number of preocclusion spheres were present in the lungs after 10 h, the bulk of which had originated from other organs than the infarct. These results quantify an important limitation to the use of microsphere distribution as a method for tissue blood flow measurements in infarcted myocardium when the period of coronary artery occlusion exceeds a few hours.

Congenital pseudarthrosis of the leg. Late results

Forty-six patients with congenital pseudarthrosis of the leg were followed for twelve years or more. Forty of these patients were examined, interviewed, or both from 1974 to 1975. Congenital pseudarthrosis is a condition most often combined with neurofibromatosis. In neurofibromatosis the prognosis of the pseudarthrosis is dependent on the roentgenographic type. Of the procedures used, insertion of intramedullary rods and grafting gave the highest rate of union. Atrophy, shortening, valgus deformity, and limited range of motion complicated the functional results.

Congenital pseudarthrosis of the tibia and neurofibromatosis

On the basis of 21 cases of congenital pseudarthrosis of the tibia, which were radiologically typed and later personally examined, it was found that all cases of the dysplastic type also showed evidence of neurofibromatosis. No evidence of neurofibromatosis was found among the cystic and the clubfoot type of pseudarthroses.

pH Dependence and Cofactor Requirements of Photochemical Reactions in Maize Chloroplasts

The pH dependence of the photoreduction of ferricyanide and the photoreduction of NADP from water and photosystem I activity have been compared in isolated chloroplasts from mesophyll and bundle sheath cells of Zea mays. The maximum activity of photoreduction of ferricyanide occurs at pH 8.5 in isolated mesophyll chloroplasts. The addition of methylamine does not cause a marked shift in the pH maximum, but brief sonication lowers the pH maximum to 7.0. In contrast, isolated bundle sheath chloroplasts have a pH maximum at 7.0 and the shape of the pH versus activity curve is similar to that of sonicated mesophyll chloroplasts. When photoreduction of ferricyanide by the isolated chloroplasts is measured at their pH maxima, the values for bundle sheath chloroplasts are about half those of methylamine-treated mesophyll chloroplasts on a chlorophyll basis.The pH maxima for the photoreduction of NADP from water and photosystem I activity are similar in both mesophyll and bundle sheath chloroplasts with maximum activity occurring at pH 7.0 in both cases. In the presence of added plastocyanin and ferredoxin NADP-reductase, the photosystem I activities of both sonicated mesophyll and sonicated bundle sheath chloroplasts are significantly higher than those of the unsonicated preparations. On a chlorophyll basis, photosystem I activity of bundle sheath chloroplasts is at least twice that of mesophyll chloroplasts.

Photosystem II Activity in Agranal Bundle Sheath Chloroplasts from Zea mays

The photochemical activities of chloroplasts isolated from bundle sheath and mesophyll cells of maize (Zea mays var. DS606A) have been measured. Bundle sheath chloroplasts are almost devoid of grana, except in very young leaves, while mesophyll chloroplasts contain grana at all stages of leaf development.Chloroplast fragments isolated from bundle sheath cells showed a light-dependent reduction of potassium ferricyanide, 2, 6-dichlorophenolindophenol, mammalian cytochrome c, plastocyanin, and Euglena cytochrome c(552). These activities were inhibited by 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea at 1.25 micromolar. However, the photoreduction of NADP from water was extremely low or absent, except in chloroplasts from very young leaves, and the capacity for NADP reduction appeared to be related to the degree of grana formation.Photosystem I activity was present in bundle sheath chloroplast preparations at all stages of leaf growth and senescence examined. However, the activity was lower than in isolated mesophyll chloroplasts. NADPH diaphorase activity was comparable in both types of chloroplast.Chloroplasts isolated from bundle sheath cells of plants grown under a variety of conditions, including continuous and intermittent light, high and low light intensities, and high temperature, exhibited photosystem II activity.

Nicotinamide adenine dinucleotide phosphate photoreduction from water by agranal chloroplasts isolated from bundle sheath cells of maize

Photoreduction of NADP from water in agranal chloroplasts isolated from the leaf bundle sheath cells of Zea mays (var. DS 606A) or Sorghum bicolor (var. Texas 610) was dependent upon addition of plastocyanin as well as ferredoxin. Activity was further increased by the addition of ferredoxin NADP-reductase. Saturation for plastocyanin was reached at about 6 micromolar. In contrast, grana-containing chloroplasts isolated from leaf mesophyll cells of these plants or from pea (Pisum sativum L.) leaves did not require either plastocyanin or ferredoxin NADP-reductase for NADP photoreduction from water, although with some preparations plastocyanin stimulated the activity.Photosystem I activity, which was low in washed preparations of bundle sheath chloroplasts, was also stimulated by plastocyanin. The effect of plastocyanin on photosystem I activity in the grana-containing chloroplasts was similar to that on NADP photoreduction from water.In the presence of plastocyanin, the rates of NADP photoreduction from water were about the same in the agranal and granal chloroplasts, but photosystem I activity was considerably higher in bundle sheath chloroplasts. In these chloroplasts photosystem II appeared to limit the rate of NADP photoreduction.The results indicated that the agranal bundle sheath chloroplasts reduced plastocyanin via photosystem II and oxidized it via photosystem I. Both types of maize chloroplast photoreduced oxidized plastocyanin, but in the presence of methyl viologen, reduced plastocyanin was photo-oxidized only by the bundle sheath chloroplasts.

Photoreduction and Oxidation of Cytochrome f in Bundle Sheath Cells of Maize

The photo-oxidation of cytochrome f (cytochrome c(554)) in bundle sheath cells isolated from leaves of maize (Zea mays var. DS 606A) has been compared with that in intact maize leaf and in isolated pea leaf cells (Pisum sativum L.). In all cases, illumination with red light caused a negative absorbance change at 554 nm which was attributed to the oxidation of cytochrome f. The extent of this change was greater using monochromatic red light at wavelengths above 700 nm compared with wavelengths below 700 nm. 3-(3,4-Dichlorophenyl)-1, 1-dimethylurea abolished this difference in bundle sheath cells. After illumination for 1 minute or longer in bundle sheath cells, reduction of cytochrome f in the dark was rapid only if the wavelength of the illuminating light was below 700 nm. In the presence of 3-(3,4-dichlorophenyl)-1, 1-dimethlyurea, reduction was slow after illumination at all wavelengths.Cytochrome f photo-oxidation was also followed in cells of a mutant of Chlamydomonas reinhardi, ac-21, which has isolated chloroplasts that exhibit photochemical reactions similar to those shown by isolated bundle sheath chloroplasts. No evidence was obtained for photoreduction of cytochrome f in the mutant.It was concluded that in the chloroplast of the intact bundle sheath cell of maize there is electron flow between photosystem II and cytochrome f resulting in photoreduction of the cytochrome.