Identification of amino acid residues lining the pore of a gap junction channel.

Gap junctions represent a ubiquitous and integral part of multicellular organisms, providing the only conduit for direct exchange of nutrients, messengers and ions between neighboring cells. However, at the molecular level we have limited knowledge of their endogenous permeants and selectivity features. By probing the accessibility of systematically substituted cysteine residues to thiol blockers (a technique called SCAM), we have identified the pore-lining residues of a gap junction channel composed of Cx32. Analysis of 45 sites in perfused Xenopus oocyte pairs defined M3 as the major pore-lining helix, with M2 (open state) or M1 (closed state) also contributing to the wider cytoplasmic opening of the channel. Additional mapping of a close association between M3 and M4 allowed the helices of the low resolution map (Unger et al., 1999. Science. 283:1176-1180) to be tentatively assigned to the connexin transmembrane domains. Contrary to previous conceptions of the gap junction channel, the residues lining the pore are largely hydrophobic. This indicates that the selective permeabilities of this unique channel class may result from novel mechanisms, including complex van der Waals interactions of permeants with the pore wall, rather than mechanisms involving fixed charges or chelation chemistry as reported for other ion channels.

Application of SCAM (substituted cysteine accessibility method) to gap junction intercellular channels.

The pore-lining residues of gap junction channels determine their permeability to ions and small cellular metabolites. These residues can be identified through systematic cysteine substitution and accessibility analysis, commonly known as SCAM (Substituted Cysteine Accessibility Method). However, application of this technique to intercellular channels is more complicated than for their transmembrane counterparts. We have utilized a novel dual-oocyte perfusion device to apply cysteine reagents to the cytoplasmic face of paired, voltage-clamped Xenopus oocytes. In this configuration, a large and irreversible cysteine reagent MBB (maliemidobutyryl biocytin, mw 537) was shown to readily traverse the gap junction pore and induce conductance changes upon reaction of accessible sites. Of the 11 reactive sites identified, 6 were located in M3, where they span the bilayer. They display a periodicity characteristic of the tilted helix that lines the pore in the gap junction structure of Unger et al. (1999). Access to several of the other sites was attributed to aqueous crevices between transmembrane helices. Reactive sites were slightly different than those identified for gap junction hemichannels (Zhou et al. 1997), suggesting that conformational changes occur upon docking.

The effect of fibrin sealant on the healing of laser-resurfaced skin.

BACKGROUND: Fibrin sealant is an effective hemostatic agent and a useful tissue sealant. Studies have also suggested that fibrin sealant may accelerate the normal wound-healing process. OBJECTIVE: This study was designed to ascertain whether fibrin sealant would enhance wound healing after CO(2) laser resurfacing in a guinea pig model. METHODS: The CO(2) laser was used to create equal areas of skin resurfacing on both sides of 14 Dunkin Hartley guinea pigs. Fibrin sealant was applied to the treatment side, whereas bacitracin was applied to the control side. Biopsies of these areas were performed on days 1, 3, 7, and 10. A histologic evaluation was performed with the use of a grading scale that compared acute and chronic inflammation, granulation tissue, collagen deposition, and epidermal regeneration. RESULTS: The wounds treated with fibrin sealant demonstrated a statistically significant reduction in the degree of acute and chronic inflammation as well as collagen deposition. At day 7, fibrin sealant was noted to enhance neovascularization and result in a slight delay in reepithelialization. All wounds were completely reepithelialized at day 10. No wound infections or other complications were noted as a result of the application of fibrin sealant. CONCLUSIONS: Although wound healing was not accelerated, the application of fibrin sealant after CO(2) laser resurfacing diminished the acute and chronic inflammatory response, enhanced neovascularization, and reduced collagen accumulation. Further research is needed to assess whether the effects of fibrin sealant noted in this study result in improved cosmetic healing after CO(2) laser resurfacing. (Aesthetic Surg J 2001;21:509-517.).

Cerebral morphometry and clozapine treatment in schizophrenia.

Studies of brain morphology in schizophrenia may be informative about basic pathophysiologic processes, provide clinically useful indicators of treatment response, and lead to the identification of markers for selective treatment effects. This paper reviews findings from magnetic resonance imaging studies of patients with schizophrenia conducted at Hillside Hospital, with special attention to (1) findings that have helped distinguish patients who respond well to typical neuroleptics from those who have gone on to trials of clozapine, (2) the capacity of morphological measures to predict clozapine treatment response, and (3) the possibility that selective hypertrophy of striatal structure may be caused by chronic treatment with typical neuroleptics, but not by clozapine.

The use of clozapine in neurologic disorders.

The advent of clozapine has marked a major advance in the treatment of schizophrenia because of its low incidence of extrapyramidal side effects and superior efficacy. Because of a relatively high incidence of agranulocytosis, approved indications for use are limited to treatment-refractory or neuroleptic-intolerant patients with schizophrenia. However, an emerging body of literature suggests that clozapine may be preferable to typical neuroleptics for treating psychosis in certain neurologic disorders. In addition, clozapine may have a place in the treatment of movement disorders that are caused by or are a result of the pharmacologic treatment of some neurologic illnesses. In general, clozapine doses used in these settings are lower than that for treating psychosis in schizophrenia. This article reviews the experience with clozapine in selected neurologic disorders.

Long-term stability of Teflon orbital implants.

Teflon orbital floor implants have become controversial owing to reports of implant-related complications. To determine the actual incidence of Teflon implant-related complications and factors associated with complications, we conducted a long-term follow-up study of 77 selected patients. We obtained data on 35 implants in 31 patients with a mean follow-up period of 16 years, representing an experience of 528 patient-implant years. The short-term complication rate (within 1 month of surgery) was 3.9 percent. The long-term complication rate was 2.8 percent. Concomitant antral packing and implantation of Teflon sheet were associated with a markedly higher risk of implant pocket infection. There was no case of implant migration with proper fixation. Facial growth was normal in three children in the series. We conclude that Teflon sheet is well-tolerated in the orbit in the long term. The low complication rate can be further reduced with proper fixation of the implant and avoidance of antral packing at the time of implantation.

Retroconversion of malignant immature teratomas of the ovary after chemotherapy.

Two cases are reported in which a malignant, immature teratoma of the ovary retroconverted to a benign mature teratoma following chemotherapy. The literature is reviewed and possible explanations for this phenomenon are discussed.

The management of a pelvic lymphocele by the use of a percutaneous indwelling catheter inserted with ultrasound guidance.

The management of a pelvic lymphocele is initially expectant. Surgical intervention is not utilized until major problems occur. The first reported case of a postsurgical pelvic lymphocele managed by the use of a percutaneous indwelling catheter inserted and monitored with ultrasound guidance is presented. If this technique proves to be generally successful with more experience, intervention could be considered at an earlier point since a major surgical procedure is not involved.

Effect of intraocular gas on intraocular pressure.

The problems encountered in measuring intraocular pressure in eyes containing a compressible gas and the problem of determining the effect of changes in ambient atmospheric pressure on such eyes have been studied experimentally in enucleated human eyes and living rabbit eyes, and studied theoretically using the Friedenwald pressure-volume relationship, Boyle law, and the Goldmann equation of aqueous humor inflow and outflow. It has been concluded that high displacement tonometry, such as Schiötz tonometry will give false low measurements of intraocular pressure under these circumstances, and that there is no reliable way to correct these erroneous measurements other than to carry out tonometry with a low displacement instrument such as the Goldmann tonometer, the Perkins tonometer, or the Mackay-Marg tonometer. It was noted that large changes in intraocular pressure occur during rapid changes in ambient atmospheric pressure. It was concluded from theoretical considerations that persons with an eye containing 1 cu cm or more of a compressible gas should be advised to avoid air travel.