Enhancement of fracture healing after citrulline supplementation in mice.

Around 10 % of long bone fractures show inadequate bone healing resulting in non-union development. A deregulated arginine-citrulline-nitric oxide metabolism caused by a poor nutritional status of the patients is a risk factor for non-unions. Additionally, previous research in mice with a disrupted arginine to citrulline conversion showed delayed healing. The study hypothesis was that stimulating said metabolism could positively influence the healing process through promotion of collagen synthesis and angiogenesis. Adult wild-type mice underwent a femur osteotomy and plate-screw osteosynthesis. Mice were randomly divided into three groups and received daily oral supplementation of arginine, citrulline or 0.9 % saline (control). Body weight and food intake were measured daily. After 14 d, the mice were euthanised and femora collected. Callus formation was assessed by micro-computed tomography and concentrations of amino acids and enzymes in the femora were measured. Only citrulline-treated mice showed significantly increased bridging of the fracture gap when compared to control mice. Femur citrulline and ornithine concentrations were increased in citrulline-treated animals. qPCR showed significantly decreased expression of inflammatory markers, whereas increased expression of angiogenic and collagen-producing factors was observed in citrulline-treated mice. Although food intake did not show any difference between the three groups, animals treated with citrulline showed a weight gain of 0.3 g, compared with a 0.1 g decline in the control group. Daily oral citrulline supplementation stimulated callus formation and improved the inflammatory response, positively contributing to the enhanced healing response. Finally, the increased weight gain pointed toward a better post-operative recovery.

Is the AO guideline for postoperative treatment of tibial plateau fractures still decisive? A survey among orthopaedic surgeons and trauma surgeons in the Netherlands.

INTRODUCTION: The standard aftercare treatment (according to the AO guideline) for surgically treated trauma patients with fractures of the tibial plateau is non-weight bearing or partial weight bearing for 10-12 weeks. The purpose of this study was to investigate the current state of practice among orthopaedic surgeons and trauma surgeons in choosing the criteria and the time period of restricted weight bearing after surgically treated tibial plateau fractures. MATERIALS AND METHODS: A web-based survey was distributed among members of the Dutch Trauma Society and Dutch Orthopaedic Society to identify the most commonly applied protocols in terms of the post-operative initiation and level of weight bearing in patients with tibial plateau fractures. RESULTS: One hundred and eleven surgeons responded to the survey. 72.1% of the respondents recommended starting weight bearing earlier than the 12 weeks recommended by the AO guideline; 11.7% recommended starting weight bearing immediately, 4.5% after 2 weeks and 55.9% after 6 weeks. Moreover, 88.7% of the respondents reported deviating from their own local protocol. There is little consensus about the definition of 100% weight bearing and how to build up weight bearing over time. CONCLUSION: This study demonstrates that consensus about the weight bearing aftercare for tibial plateau fractures are limited. A large majority of surgeons do not follow the AO guideline or their own local protocol. More transparent criteria and predictors are needed to design optimal weight-bearing regimes for the aftercare of tibial plateau fractures.

Determining scaphoid waist fracture union by conventional radiographic examination: an analysis of reliability and validity.

INTRODUCTION: Conventional radiographic imaging is the first imaging tool of choice in scaphoid fractures. The majority of undisplaced scaphoid waist fractures unite after 6 weeks of cast immobilization. We hypothesized that conventional radiographic imaging at 6 weeks after injury can both accurately and reliably predict union in undisplaced scaphoid waist fractures. MATERIALS AND METHODS: Fleiss' kappa statistics were used concerning the opinions of four observers reviewing 47 sets of good-quality scaphoid radiographs of undisplaced scaphoid waist fractures. As reference standard for union, radiographs were taken at a minimum of 6 months after injury to determine validity. RESULTS: Overall agreement was defined as moderate. (κ = 0.583) "No consolidation" (κ = 0.816), "full consolidation" (κ = 0.517) and "partial consolidation" (κ = 0.390) were defined as good, moderate and fair agreement, respectively. The average sensitivity and specificity of diagnosing scaphoid waist fracture union on standard scaphoid radiographs were 0.65 and 0.67, respectively. The positive predictive value for diagnosing union was 0.93 and the negative predictive value was 0.22. CONCLUSIONS: Conventional radiographic imaging is accurate and moderately reliable in diagnosing union, and reliable but inaccurate in diagnosing nonunion of scaphoid waist fractures at 6 weeks follow-up.

Biochemical evidence for gap junctions and Cx43 expression in immortalized human chondrocyte cell line: a potential model in the study of cell communication in human chondrocytes.

OBJECTIVE: The development of chondrocytic cell lines has enabled the investigation of the role of cellular phenotype and mechanisms in articular cartilage biology and physiopathology of several rheumatic diseases. Among them, the T/C-28a2 cell line has become a common tool in cartilage research. Recent results from our group have revealed that primary human chondrocytes in tissue and in monolayer culture contain high levels of connexin 43 (Cx43) and are able to directly communicate through gap junction (GJ) channels. These results challenge the existing thesis of cartilage physiology, that chondrocytes do not have the capacity to physically communicate with each other. Established cell lines offer the advantage of convenience and uniformity; however, the establishment process may cause a disruption of GJ. This study was performed to investigate if T/C-28a2 cells contain Cx43 protein and form functional channels. METHODS: Cx43 was characterized by RT-qPCR, Western blotting, and immunohistochemistry (IHC). Electrophysiology experiments, Lucifer Yellow (LY) uptake, electroporation in situ and scrape loading assay were performed to test the functionality of GJs. RESULTS: T/C-28a2 cells express Cx43. Electrophysiology experiments and LY uptake confirmed the capacity of these cells to communicate through GJ channels, although these cells contain significant levels of active c-Src kinase, presumably due to their immortalization with the Simian Virus 40 large T antigen. The results were validated using primary chondrocytes (PC). CONCLUSIONS: These results reveal that the T/C-28a2 line may provide a useful in vitro model for the study of Cx43 function and cell communication to understand the physiology of chondrocytes and cartilage.

The effects of low-intensity pulsed ultrasound and pulsed electromagnetic fields bone growth stimulation in acute fractures: a systematic review and meta-analysis of randomized controlled trials.

INTRODUCTION: The aim of this systematic review and meta-analysis was to evaluate the best currently available evidence from randomized controlled trials comparing pulsed electromagnetic fields (PEMF) or low-intensity pulsed ultrasound (LIPUS) bone growth stimulation with placebo for acute fractures. MATERIALS AND METHODS: We performed a systematic literature search of the medical literature from 1980 to 2013 for randomized clinical trials concerning acute fractures in adults treated with PEMF or LIPUS. Two reviewers independently determined the strength of the included studies by assessing the risk of bias according to the criteria in the Cochrane Handbook for Systematic Reviews of Interventions. RESULTS: Seven hundred and thirty-seven patients from 13 trials were included. Pooled results from 13 trials reporting proportion of nonunion showed no significant difference between PEMF or LIPUS and control. With regard to time to radiological union, we found heterogeneous results that significantly favoured PEMF or LIPUS bone growth stimulation only in non-operatively treated fractures or fractures of the upper limb. Furthermore, we found significant results that suggest that the use of PEMF or LIPUS in acute diaphyseal fractures may accelerate the time to clinical union. CONCLUSIONS: Current evidence from randomized trials is insufficient to conclude a benefit of PEMF or LIPUS bone growth stimulation in reducing the incidence of nonunions when used for treatment in acute fractures. However, our systematic review and meta-analysis suggest that PEMF or LIPUS can be beneficial in the treatment of acute fractures regarding time to radiological and clinical union. PEMF and LIPUS significantly shorten time to radiological union for acute fractures undergoing non-operative treatment and acute fractures of the upper limb. Furthermore, PEMF or LIPUS bone growth stimulation accelerates the time to clinical union for acute diaphyseal fractures.

Multiplanar reconstruction computed tomography for diagnosis of scaphoid waist fracture union: a prospective cohort analysis of accuracy and precision.

OBJECTIVE: To examine reliability and validity concerning union of scaphoid fractures determined by multiplanar reconstruction computed tomography randomized at 6, 12, and 24 weeks after injury. MATERIALS AND METHODS: We used Fleiss' kappa to measure the opinions of three observers reviewing 44 sets of computed tomographic scans of 44 conservatively treated scaphoid waist fractures. We calculated kappa for the extent of consolidation (0-24 %, 25-49 %, 50-74 %, or 75-100 %) on the transverse, sagittal and coronal views. We also calculated kappa for no union, partial union, and union, and grouped the results for 6, 12, and 24 weeks after injury. As the reference standard for union, CT scans were performed at a minimum of 6 months after injury to determine validity. RESULTS: Overall inter-observer agreement was found to be moderate (κ = 0.576). No union (κ = 0.791), partial union (κ = 0.502), and union (κ = 0.683) showed substantial, moderate, and substantial agreement, respectively. The average sensitivity of multiplanar reconstruction CT for diagnosing union of scaphoid waist fractures was 73 %. The average specificity was 80 %. CONCLUSIONS: Our results suggest that multiplanar reconstruction computed tomography is a reliable and accurate method for diagnosing union or nonunion of scaphoid fractures. However, inter-observer agreement was lower with respect to partial union.

Gap junction permeability: selectivity for anionic and cationic probes.

Gap junction channels formed by different connexins exhibit specific permeability to a variety of larger solutes including second messengers, polypeptides, and small interfering RNAs. Here, we report the permeability of homotypic connexin26 (Cx26), Cx40, Cx43, and Cx45 gap junction channels stably expressed in HeLa cells to solutes with different size and net charge. Channel permeability was determined using simultaneous measurements of junctional conductance and the cell-cell flux of a fluorescent probe. All four connexins allowed passage of both cationic and anionic probes, but the transfer rates were connexin dependent. The negatively charged probes [Lucifer yellow (LY; median axial diameter 9.9 Å, charge -2), carboxyfluorescein (CF; 8.2 Å; -2), and Alexa Fluor350 (AF350, 5.4 Å; -1)] exhibited the following permeability order: Cx43 > Cx45 > Cx26 > Cx40. In contrast, for the positively charged species permeability, the orders were as follows: Cx26 ≈ Cx43 ≈ Cx40 ≈ Cx45 for N,N,N-trimethyl-2-[methyl-(7-nitro-2,1,3-benzoxadiol-4-yl) amino] ethanaminium (NBD-m-TMA; 5.5 Å, +1) and Cx26 ≥ Cx43 ≈ Cx40 > Cx45 for ethidium bromide (10.3 Å, +1). Comparison of probe permeability relative to K(+) revealed that Cx43 and Cx45 exhibited similar permeability for NBD-m-TMA and AF350, indicating weak charge selectivity. However, lesser transfer of CF and LY through Cx45 relative to Cx43 channels suggests stronger size-dependent discrimination of solute. The permeability of NBD-m-TMA for Cx40 and Cx26 channels was approximately three times higher than to anionic AF350 despite the fact that both have similar minor diameters, suggesting charge selectivity. In conclusion, these results confirm that channels formed from individual connexins can discriminate for solutes based on size and charge, suggesting that channel selectivity may be a key factor in cell signaling.

Age-associated differences in the inhibition of mitochondrial permeability transition pore opening by cyclosporine A.

BACKGROUND: Inhibiting mitochondrial permeability transition pore (mPTP) opening is a key protection of the myocardium from ischemia/reperfusion (I/R) injury. Here, we investigated age-associated differences in the ability of cyclosporine A (CsA) to protect the heart and to modulate mPTP opening during I/R injury in vivo and its opening induced by reactive oxygen species (ROS) in vitro. METHODS: Fischer 344 male rats were assigned from their respective age groups, young or old groups, to (1) I/R or (2) I/R+CsA. All animals were subjected to 30 min of ischemia following 120 min of reperfusion to determine myocardial infarct size in vivo. To measure mPTP opening in vivo, left ventricular tissues were collected 10 min after reperfusion and nicotinamide adenine dinucleotide (NAD(+)) levels were measured. In parallel experiments, rat ventricular myocytes were prepared from young and old hearts, loaded with tetramethylrhodamine ethylester and then subjected to oxidative stress in the presence or absence of CsA, and the mPTP opening time was measured using laser scanning confocal microscopy. RESULTS: CsA reduced myocardial infarct size in young I/R rats. Whereas CsA failed to significantly affect myocardial infarct size in old I/R rats, NAD(+) levels were better preserved in young CsA-treated rats, but this relative improvement was not observed in old rats. CsA also significantly prolonged the time necessary to induce mPTP opening in young cardiomyocytes, but not in cardiomyocytes isolated from the old rats. CONCLUSIONS: mPTP regulation is dysfunctional in the aged myocardium and this could account for loss of cardioprotection with aging.

Coupling an HCN2-expressing cell to a myocyte creates a two-cell pacing unit.

We examined whether coupling of a ventricular myocyte to a non-myocyte cell expressing HCN2 could create a two-cell syncytium capable of generating sustained pacing. Three non-myocyte cell types were transfected with the mHCN2 gene and used as sources of mHCN2-induced currents. They were human mesenchymal stem cells and HEK293 cells, both of which express connexin43 (Cx43), and HeLa cells transfected with Cx43. Cell-cell coupling between heterologous pairs increased with time in co-culture, and hyperpolarization of the myocyte induced HCN2 currents, indicating current transfer from the mHCN2-expressing cell to the myocyte via gap junctions. The magnitude of the HCN2 currents recorded in myocytes increased with increasing junctional conductance. Once a critical level of electrical cell-cell coupling between myocytes and mHCN2 transfected cells was exceeded spontaneous action potentials were generated at frequencies of approximately 0.6 to 1.7 Hz (1.09 +/- 0.05 Hz). Addition of carbenoxolone (200 microM), a gap junction channel blocker, to the media stopped spontaneous activity in heterologous cell pairs. Carbenoxolone washout restored activity. Blockade of HCN2 currents by 100 microM 9-amino-1,2,3,4-tetrahydroacridine (THA) stopped spontaneous activity and subsequent washout restored it. Neither THA nor carbenoxolone affected electrically stimulated action potentials in isolated single myocytes. In summary, the inward current evoked in the genetically engineered (HCN2-expressing) cell was delivered to the cardiac myocyte via gap junctions and generated action potentials such that the cell pair could function as a pacemaker unit. This finding lays the groundwork for understanding cell-based biological pacemakers in vivo once an understanding of delivery and target cell geometry is defined.

[Athletes with exercise-related pain at the medial side of the lower leg]. / Sporters met inspanningsgerelateerde pijn aan de mediale zijde van het onderbeen.

Two patients were diagnosed with exercise-related pain at the medial side of the lower leg. The first patient, an 18-year-old woman who had expanded her athletic activities extensively, had developed pain at the inner side of the distal third portion of the left lower leg. She showed over-pronation of the ankle during running. A 3-phase bone scintigram revealed diffuse uptake of the tracer covering a large portion of the medial tibia margin. Based on this evidence, a diagnosis of periostalgia was made. She recovered after a period of relative calf massages and used insoles. The second patient was a 28-year-old male endurance runner who developed pain at the medial shin after intensifying his training regimen. The periods without pain during running became increasingly shorter, and the medial side of the lower leg became sore and tense. Intracompartmental pressure measurements indicated exercise-related posterior deep compartment syndrome of the calf. The patient recovered after fasciotomy. In athletes, exercise-related symptoms of the medial side of the lower leg can be usually attributed to the tibial periosteum or tendons of the deep calfmusculature, tibial stress reaction or fracture, or a compartment syndrome of the deep calf. Surgery is indicated for chronic compartment syndrome, but conservative therapy provides favourable outcomes in the other types of disorders. The optimal conservative therapeutic approach is unknown, but it is advisable to temporary reduce symptom-provoking athletic activity and modify any risk factors present. Ankle over-pronation during running is considered a very relevant intrinsic risk factor.

[Earlier weight-bearing mobilisation after fracture fixation]. / Eerder belast mobiliseren na fractuurfixatie.

Almost all the literature dictates a period of non-weight-bearing after surgical treatment of articular and peri-articular fractures of the pelvis and lower extremities. This is followed by partial weight-bearing which is based on the number of weeks after surgery. However, none of these recommendations are based on evidence. When taking muscle force and gravity into account, non-weight-bearing is actually impossible. In addition, lack of patient compliance, lack of muscle force in the elderly and four-fold energy expenditure make it almost impossible to ensure that patients will adhere to their surgeon's restrictions. Based on our experiences in a large cohort of patients with fractures of the pelvis and lower extremities, we see no drawbacks in permissive weight-bearing and early recovery in most cases. We strongly believe that most patients are able to listen to their body and understand body awareness, while the creation of a safe environment makes more personalised follow-up treatment possible.

Formation of heterotypic gap junction channels by connexins 40 and 43.

Gap junctions formed between transfected cells expressing connexin (Cx) 40 and Cx43 (Cx43-RIN, Cx40-HeLa, and Cx43-HeLa) revealed a relationship, g(j)=f(V(j)), at steady state, that is typified by a nonsymmetrical behavior similar to that previously reported for other heterotypic channels (gap junction conductance [g(j)]; transjunctional voltage [V(j)]). The unitary conductance of the channels was sensitive to the polarity of V(j). A main state conductance of 61 pS was found when the Cx43 cell was stepped positively or the Cx40 cell negatively (V(j)=70 mV); the reverse polarities yielded a conductance of 100 pS. These heterotypic channels were permeable to carboxyfluorescein. In addition, two other heterotypic forms are illustrated to demonstrate that endogenous Cx45 expression cannot explain the results. The demonstration of heterotypic Cx40-Cx43 channels may have implications for the propagation of the electrical impulse in heart. For example, they may contribute to the slowing of the impulse propagation through the junctions between Purkinje fibers and ventricular muscle.

[Coagulation disorders in patients with trauma to the skull and brain: a frequent and potentially fatal combination]. / Stollingsstoornissen bij patiënten met schedel-hersentrauma: een frequente en potentieel fatale combinatie.

Abnormalities in blood coagulation are relatively common after traumatic brain injury (TBI) and play an important role in the morbidity and mortality after head injuries. Exposure oftissue factor, which is abundantly present in brain tissue, is the initiator of the coagulation cascade and plays an important role in the pathogenesis of coagulopathy after TBI. Coagulopathy after TBI is actually a manifestation of the disseminated intravascular coagulation (DIC) syndrome. The interplay between hypothermia, acidosis and progressive coagulopathy, referred to as the 'lethal triad', results in high mortality. This necessitates damage control in the treatment of such TBI patients. Repeated laboratory evaluation of the coagulation parameters in TBI patients is indicated, even if the initial values are normal. The DIC score, a combination of frequently used coagulation parameters, is not only a measure of the coagulopathy but can also predict the outcome and prognosis following TBI. Primary and secondary prevention of coagulopathy together with timely and effective intervention are the most important elements in the treatment of coagulation disorders. Nevertheless, the risk of death remains high.

Four-Corner Concept: CT-Based Assessment of Fracture Patterns in Distal Radius.

Operative treatment using plate fixation is an important adjunct in the treatment of distal radius fractures, although the evidence for its superiority over other modalities remains limited. We propose a new concept for fractures of the distal radius, based on the three-column model of the distal radius, and on the expanding knowledge about the different fracture patterns obtained by evaluation of the distal radius by computed tomographic (CT) scan. All fracture types can be characterized by subdividing the wrist joint into four corners, each with its own characteristics in terms of mobility, stability, and transfer of forces in the intact distal radius. Recognition of the specific fracture types based on this four-corner concept enables a tailored approach to treatment.

Dorsal or Volar Plate Fixation of the Distal Radius: Does the Complication Rate Help Us to Choose?

BACKGROUND: Internal fixation with plates is a reliable fixation technique for the treatment of distal radius fractures. An ongoing discussion exists whether volar or dorsal plating is the appropriate technique. In clinical practice, volar plate fixation is usually preferred because of the assumed lower complication frequency. However, recent studies with the newer generation low-profile dorsal plates reported lower complication rates. PURPOSE: The aim of our study was to evaluate the differences in complication rates between volar and dorsal plate for the treatment of distal radius fractures in adult patients. PATIENTS AND METHODS: A total of 214 patients with acute distal radius fractures were included in this retrospective study with a minimum 2 years of follow-up. In total, 123 patients were treated with dorsal plate fixation and 91 patients with volar plate fixation. Our primary study outcome was complication rate. RESULTS: The overall risk for complications was 15.4% in the dorsal group and 14.3% in the volar group (p = 0.81). A total of 19 patients had implant removal due to complications: 11 patients in the dorsal group and 8 patients in the volar group (p = 0.97). CONCLUSION: There is no preferred plate fixation technique based on these study results. In our opinion, decision for type of plate fixation should be based on fracture type and surgeon's experience with the specific approach and plate types. LEVEL OF EVIDENCE: Therapeutic level III.

Is early Weight Bearing Allowed in Surgically Treated Talar Neck Fractures?

INTRODUCTION: Non-or partial weight bearing is frequently the standard treatment after peri-articular lower extremity fractures. Displaced talar neck fractures are severe injuries compromising vascularity of the corpus and consequently are at risk for non-union and avascular necrosis, the main reason to restrict weight bearing for up to three months according to most literature. CASE PRESENTATION: We report a case of a 31-year old male with a high impact car accident. His pelvic ring and Hawkins II talar fracture were treated by open reduction and internal fixation. Rehabilitation was based on permissive weight bearing following wound healing. His fractures healed uneventfully and he was able to run freely, without any discomfort within 8 weeks. Radiological evaluation of the talus showed complete bone healing without signs of avascular necrosis. At one year follow-up, the patient is free of the symptoms. CONCLUSION: We might consider changing the restricted or non-weight bearing protocol in surgically treated talar neck fractures at our centre and allow early weight bearing, based on body awareness and the creation of a safe environment during the rehabilitation phase.

Deficiency of inducible and endothelial nitric oxide synthase results in diminished bone formation and delayed union and nonunion development.

BACKGROUND: Between 5% and 10% of all fractures fail to heal adequately resulting in nonunion of the fracture fragments. This can significantly decrease a patient's quality of life and create associated psychosocial and socio-economic problems. Nitric oxide (NO) and nitric oxide synthases (NOS) have been found to be involved in fracture healing, but until now it is not known if disturbances in these mechanisms play a role in nonunion and delayed union development. In this study, we explored the role of endothelial and inducible NOS deficiency in a delayed union model in mice. MATERIALS AND METHODS: A 0.45mm femur osteotomy with periosteal cauterization followed by plate-screw osteosynthesis was performed in the left leg of 20-24week old wild type, Nos2(-/-) and Nos3(-/-) mice. Contralateral unfractured legs were used as a control. Callus volume was measured using micro-computed tomography (µCT) after 28 and 42days of fracture healing. Immuno histochemical myeloperoxidase (MPO) staining was performed on paraffin embedded sections to assess neutrophil influx in callus tissue and surrounding proximal and distal marrow cavities of the femur. After 7 and 28days of fracture healing, femurs were collected for amino acid and RNA analysis to study arginine-NO metabolism. RESULTS: With µCT, delayed union was observed in wild type animals, whereas in both Nos2(-/-) and Nos3(-/-) mice nonunion development was evident. Both knock-out strains also showed a significantly increased influx of MPO when compared with wild type mice. Concentrations of amino acids and expression of enzymes related to the arginine-NO metabolism were aberrant in NOS deficient mice when compared to contralateral control femurs and wild type samples. DISCUSSION AND CONCLUSION: In the present study we show for the first time that the absence of nitric oxide synthases results in a disturbed arginine-NO metabolism and inadequate fracture healing with the transition of delayed union into a nonunion in mice after a femur osteotomy. Based on these data we suggest that the arginine-NO metabolism may play a role in the prevention of delayed unions and nonunions.

Effectiveness of a Multidisciplinary Clinical Pathway for Elderly Patients With Hip Fracture: A Multicenter Comparative Cohort Study.

INTRODUCTION: The use of a multidisciplinary clinical pathway (MCP) for patients with hip fracture tends to be more effective than usual care (UC). The aim of this study was to evaluate the effects of an MCP approach on time to surgery, length of stay, postoperative complications, and 30-day mortality, compared to UC. MATERIALS AND METHODS: This multicenter retrospective cohort study included patients aged 50 years or older with a proximal hip fracture who underwent surgery in one of the 6 hospitals in the Limburg trauma region of the Netherlands in 2012. Data such as demographics, process outcome measures, and clinical outcome were collected. RESULTS: This study included a total of 1193 patients (665 and 528 patients in the MCP and UC groups, respectively). There were no differences in patient demographics present. Time to surgery was significantly shorter in the MCP compared to the UC group (19.2 vs 24.4 hours, P < .01). The mean length of stay was 10 versus 12 days (P < .01). In the MCP group, significantly lower rates of postoperative complications were observed and significantly more patients were institutionalized than in the UC group. Mortality within 30 days after admission was comparable between the groups (overall mortality 6%). CONCLUSION: An MCP approach is associated with reduced time to surgery, postoperative complications, and length of stay, without a significant difference in 30-day mortality. The institutionalization rate was significantly higher in the MCP group.

Voltage sensitivity of gap junction currents in rat osteoblast-like cells.

The dependence of macroscopic gap junctional conductance (g(j)) upon transjunctional voltage (Vj) was examined in 39 paired osteoblast-like (OB) cells from primary cultures using the double whole cell patch clamp technique. OB cells were derived from calvarial explants of new-born rats. Instantaneous current-voltage (Ij-Vj) relationships of OB cell pairs (n = 6) were linear in the entire voltage range (-150 < Vj < 150 mV) examined. The steady-state Ij-Vj relationship was non-linear for V > or = +/-60 mV. The curve for the normalised steady-state junctional conductance-voltage relationship (Gss/G0-Vj) was bell-shaped, and was fitted with a two-state Boltzmann equation with a minimum conductance (Gmin) of 0.2-0.3, and a half deactivation voltage (Vo) of +/-83 mV. In two recordings unitary gap junction channel activity was observable. The linear I-V relationships revealed a single channel conductance of approximately 100 pS. Application of parathyroid hormone (10(-8) M) had no effect on the voltage dependence nor the magnitude of macroscopic currents (n = 7).

Nexal membrane permeability to anions.

The permeability of the septa of the earthworm in the median axon has been calculated for the anions fluorescein and its halogen derivatives. The values ranged from 5.4 X 10(-5) to 4 X 10(-6) cm/s. Previously, the septa had been shown to contain nexuses. By using freeze-fracture material, the surface area of nexus on the septal membranes was determined to be 4.5%, very similar to the percentage of nexus in the intercalated disk of mammalian myocardium. Plasma membrane permeability to these dyes was also calculated and shown to be much less than that of the septal membranes. In addition, an estimate of cytoplasmic binding for each dye was made, and most dyes showed little or no binding with the exception of aminofluorescein.