Voltage gating and permeation in a gap junction hemichannel

Gap junction channels are formed by members of the connexin gene family and mediate direct intercellular communication through linked hemichannels (connexons) from each of two adjacent cells. While for most connexins, the hemichannels appear to require an apposing hemichannel to open, macroscopic currents obtained from Xenopus oocytes expressing rat Cx46 suggested that some hemichannels can be readily opened by membrane depolarization [Paul, D. L., Ebihara, L., Takemoto, L. J., Swenson, K. I. & Goodenough, D. A. (1991), J. Cell Biol. 115, 1077-1089]. Here we demonstrate by single channel recording that hemichannels comprised of rat Cx46 exhibit complex voltage gating consistent with there being two distinct gating mechanisms. One mechanism partially closes Cx46 hemichannels from a fully open state, gammaopen, to a substate, gammasub, about one-third of the conductance of gammaopen; these transitions occur when the cell is depolarized to inside positive voltages, consistent with gating by transjunctional voltage in Cx46 gap junctions. The other gating mechanism closes Cx46 hemichannels to a fully closed state, gammaclosed, on hyperpolarization to inside negative voltages and has unusual characteristics; transitions between gammaclosed and gammaopen appear slow (10-20 ms), often involving several transient substates distinct from gammasub. The polarity of activation and kinetics of this latter form of gating indicate that it is the mechanism by which these hemichannels open in the cell surface membrane when unapposed by another hemichannel. Cx46 hemichannels display a substantial preference for cations over anions, yet have a large unitary conductance (approximately 300 pS) and a relatively large pore as inferred from permeability to tetraethylammonium (approximately 8.5 angstroms diameter). These hemichannels open at physiological voltages and could induce substantial cation fluxes in cells expressing Cx46.     

Molecular executors of cell death--differential intrarenal expression of Fas ligand, Fas, granzyme B, and perforin during acute and/or chronic rejection of human renal allografts

BACKGROUND: Changes in peripheral thyroid hormone concentration and metabolism can occur in euthyroid patients suffering from severe non-thyroidal illnesses. Recently, sick euthyroid syndrome has been reported in patients suffering from advanced heart failure. AIM: This study was to evaluate prospectively the presence and pathophysiological implications of sick euthyroid syndrome in moderate-to-severe chronic heart failure patients. METHODS: The study population were 199 chronic heart failure patients admitted over a 2-year period to our heart failure unit for assessment of cardiac transplantation. They were closely followed up with clinical and instrumental examinations (including clinical, hormonal, nutritional and cardiac function evaluations). Sick euthyroid syndrome was defined as a serum total triiodothyronine value of less than the lowest normal limit (< 1.23 nmol.l-1) in the presence of a normal serum thyroid stimulating hormone concentration. RESULTS: Sick euthyroid syndrome was found in 36/199 patients (18%). According to the New York Heart Association (NYHA) classification of severity of heart failure, sick euthyroid syndrome patients appear in higher NYHA classes (31% of classes III and IV, vs 7% of class I and II). Such patients also weigh less and are more frequently malnourished. Alterations in cardiac index, ventricular filling pressures, functional impairment, and the liver function parameters, were more significant in sick euthyroid syndrome than in non-sick euthyroid syndrome patients. Serum norepinephrine and atrial natriuretic factor were significantly higher, and insulin significantly lower in the sick euthyroid syndrome group. During follow-up, deaths were significantly more frequent in sick euthyroid syndrome patients (13/27, 48%) than in non-sick euthyroid syndrome (30/141, 21%; P < 0.005). In six sick euthyroid syndrome patients who underwent heart transplantation, mean total triiodothyronine values increased from 0.9 +/- 0.1 before to 1.96 +/- 0.3 nmol.l(-1)post-transplantation (P < 0.05). CONCLUSIONS: In a large and representative population of patients with moderate-to-severe heart failure, sick euthyroid syndrome shows a prevalence of 18%. Its occurrence was related to the degree of functional cardiac impairment, but was not an independent negative prognostic factor. Preliminary results indicate that heart transplantation is associated with reversibility of sick euthyroid syndrome.     

Interaction of ribosomes with membranes in vitro

Fluorescent "fusion-reporting" probe (R18) was used to study the interaction of ribosomes with membranes in vitro. The latter was incorporated both in the membranes, and ribosomes. The interaction of R18-labeled ribosomes with non-labeled liposomes (of different size and composition) or microsomes increased the fluorescence observed, i.e., the dilution of fluorescent probe took place. The dependence of interaction process on the change of liposomes indicates that the interaction between ribosomes and negatively charged liposomes was more efficient, than that with neutral ones. It is shown that ribosomes can interact with phospholipid membranes even after degradation of protein components accessible for proteins. The interaction of R18-labeled membranes with non-labeled ribosomes results in the increase of fluorescence too. Results obtained indicate to the possibility of direct interaction between ribosomes and membranes.     

Audio-vestibular manifestations of Chiari malformation and outcome of surgical decompression: a case report

Sensorineural hearing loss, tinnitus, dizziness and ataxia are recognised symptoms associated with Chiari malformations but they are rarely the presenting complaints. Patients with such symptoms are frequently referred to otolaryngologists and audiological physicians. We report a case of a 13-year-old girl who presented complaining of tinnitus and impaired hearing, and was subsequently diagnosed as having a type I Chiari malformation. Pure tone audiogram showed a mild hearing impairment on the left side and the speech audiogram was normal. Auditory brain stem responses and the electronystagmography were abnormal. The patient underwent posterior fossa decompression following which her tinnitus disappeared, the hearing problem recovered and some of the abnormal electrophysiological parameters were corrected.     

Essential hypertension: could the basic defect be in blood supply of vasomotor centre?

Various factors have been implicated in the pathogenesis of essential hypertension, although the exact cause of essential hypertension is still unknown. In this paper it is suggested that the basic pathology in essential hypertension may be an inherited defect in the blood supply of that part of reticular formation of rostral ventrolateral medulla which contains the pressor area. The posited defect is one in which the arterial branch supplying blood to the above-mentioned pressor area of vasomotor center arises from an artery which is stenosed. The other branches of this stenosed artery supply adjacent areas of medullary reticular formation concerned with other neurological functions. Due to this stenosis there is ischaemia of the pressor area resulting in increased systemic arterial pressure. During stress, the blood requirement of adjacent areas of the reticular formation (whose function is still not clearly defined) may increase, thus further decreasing blood flow to vasopressor area and increasing the cerebral ischaemic response. After a prolonged time, this increased blood pressure can cause hyaline arteriolar nephrosclerosis in kidney, which may participate in the maintenance of elevated systemic arterial pressure.     

Myosin heavy chain composition in young and old rat skeletal muscle: effects of endurance exercise

The objective of this study was to determine the effects of age and exercise on the myosin heavy chain (MHC) composition of skeletal muscle. Young (3 mo) and old (22 mo) female specific pathogen-free barrier-reared Fischer 344 rats were randomly assigned to young untrained or young trained and old untrained or old trained groups, respectively. Young trained and old trained animals performed endurance exercise training on a motorized treadmill for 8 wk. Succinate dehydrogenase activity and MHC isoforms were measured in the plantaris (Plan), lateral and medial gastrocnemius (Gast), and soleus (Sol) muscles. In sedentary animals, aging resulted in a decrease (P < 0.05) in type IIb MHC and an increase (P < 0.05) in type IIa MHC in both the Gast and Plan muscles. Also, aging resulted in a small but significant increase (approximately 4%; P < 0.05) in type I MHC in the Sol. Exercise training resulted in significant (P < 0.05) increases in Gast, Plan, and Sol succinate dehydrogenase activity in both young and old animals. Furthermore, exercise training resulted in a decrease (P < 0.05) in the percentage of type IIb MHC and an increase (P < 0.05) in the percentage of type IIa MHC in the Plan in both young and old animals. These data suggest that there is an age-related shift in locomotor muscle MHC isoforms from a faster to a slower isoform.     

Risk factors for the occurrence of postoperative suppurative-septic complications in abdominal surgery]

Nonorganic hearing loss or pseudohypacusis is a condition in which there is an apparent hearing loss without any evidence of an organic cause. In a 2-year period, 43 children were seen in our department with this diagnosis. Thirty-three of them were female and 10 were male. Their hearing loss varied from 30 dB HL to 100 dB HL. The diagnosis made on clinical impression was confirmed using the ascending and the descending mode pure tone audiometry, tympanometry, stapedial reflexes and speech audiometry. Explanation, encouragement and reassurance were the only treatment required in these patients. All the 43 patients showed normal pure tone thresholds within a period of 1 year.     

Directed inactivation of the psbI gene does not affect photosystem II in the cyanobacterium Synechocystis sp. PCC 6803

PsbI is a small, integral membrane protein component of photosystem II (PSII), a pigment-protein complex in cyanobacteria, algae and higher plants. To understand the function of this protein, we have isolated the psbI gene from the unicellular cyanobacterium Synechocystis sp. PCC 6803 and determined its nucleotide sequence. Using an antibiotic-resistance cartridge to disrupt and replace the psbI gene, we have created mutants of Synechocystis 6803 that lack the PsbI protein. Analysis of these mutants revealed that absence of the PsbI protein results in a 25-30% loss of PSII activity. However, other PSII polypeptides are present in near wild-type amounts, indicating that no significant destabilization of the PSII complex has occurred. These results contrast with recently reported data indicating that PsbI-deficient mutants of the eukaryotic alga Chlamydomonas reinhardtii are highly light-sensitive and have a significantly lower (80-90%) titer of the PSII complex. In Synechocystis 6803, PsbI-deficient cells appear to be slightly more photosensitive than wild-type cells, suggesting that this protein, while not essential for PSII biogenesis or function, plays a role in the optimization of PSII activity.