The membrane potential of vestibular dark cells is controlled by a large Cl- conductance.

The K+ secretory epithelium of the vestibular labyrinth (dark cells) was impaled with glass microelectrodes in order to test the hypothesis that it contains a large Cl- conductance. In the first series of experiments, the short-circuited epithelium was perfused on both sides by a solution containing 150 mmol/l Cl-. The membrane voltage (PD) was -18 +/- 1 mV (N = 101), showed a Gaussian distribution, and the estimated input resistance of the cell (R 'cell') was 17 +/- 3 M omega. The PD responded to 10(-4) mol/l ouabain with a depolarization, suggesting the presence of a (Na(+) + K+)-ATPase. The PD responses to Cl- steps yielded an apparent transference number tCl = 0.34 +/- 0.03 (N = 65) and those to K+ steps yielded a tK = 0.16 +/- 0.01 (N = 48). In the second series of experiments, cells presumed to be Cl(-)-depleted were impaled in Cl(-)-free solutions. The distribution of the PD was not Gaussian; PDs as negative as -90 mV were observed. Cells with a highly negative PD also had a high R 'cell'. With the addition of Cl- the PD collapsed to -19 +/- 1 mV and R collapsed to 16 +/- 3 M omega (N = 145) which are not significantly different from values obtained in the first series of experiments when cells were impaled in a solution containing 150 mmol/l Cl-. Alternating the bath perfusate between Cl(-)-free and Cl(-)-containing solutions led to large PD transients.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ca(2+)-activated nonselective cation, maxi K+ and Cl- channels in apical membrane of marginal cells of stria vascularis.

Patch clamp recordings on the apical membrane of marginal cells of the stria vascularis of the gerbil were made in the cell-attached and excised configuration. Marginal cells are thought to secrete K+ into and absorb Na+ from endolymph. Four types of channel were identified; the most frequently observed channel was a small, nonselective cation channel which was highly similar to that found in the apical membrane of vestibular dark cells (Marcus et al., (1992) Am. J. Physiol. 262, C1423-C1429). The small nonselective cation channel was equally conductive (26.7 +/- 0.3 pS; N = 49) for K+, Na+, Rb+, Li+ and Cs+, 1.6 times more permeable to NH4+, but not permeable to Cl-, Ca2+, Ba2+ or N-methyl-D-glucamine. This channel yielded linear current-voltage relations which passed nearly through the origin (intercept: -2.2 +/- 0.4 mV, N = 49) when conductive monovalent cations were present on both sides of the membrane in equal concentrations. Channel activity required the presence of Ca2+ at the cytosolic face but not the extracellular (endolymphatic) face; there was essentially no activity for cytosolic Ca2+ less than or equal to 10(-7) M Ca2+ and full activity for greater than or equal to 10(-5) M. Cell-attached recordings had a conductance of 28.6 +/- 2.2 pS (N = 6) and a reversal voltage of -2.2 +/- 5.2 mV (N = 3) which was interpreted to reflect the intracellular potential of marginal cells under the present conditions. The three other types of channel were a Cl- channel (approximately 50 pS; N = 2), a maxi-K+ channel (approximately 230 pS; N = 1), and another large channel, probably cation nonselective (approximately 170 pS; N = 1). The 27 pS nonselective cation channel may be involved in K+ secretion and Na+ absorption under stimulated conditions which produce an elevated intracellular Ca2+; however, consideration of the apparent channel density in relation to the total transepithelial K+ flux suggests that these channels are not sufficient to account for K+ secretion.     

The indirect negative inotropic effect of carbachol in beta1-adrenoceptor antagonist-treated human right atria

To find out whether indirect negative inotropic effects of carbachol (i.e. decreases in force of contraction that had been stimulated by cyclic AMP-increasing agents) might differ dependent on the agonist employed to increase contractile force in isolated human right atrium, we studied effects of carbachol on atria prestimulated with noradrenaline, terbutaline, histamine and serotonin. All four agonists increased right atrial adenylyl cyclase activity and contractile force, whereby increases for terbutaline, histamine and serotonin, but not for noradrenaline, were significantly larger in right atria from beta(1)-adrenoceptor antagonist-treated vs. non-beta(1)-adrenoceptor antagonist-treated patients. Carbachol (10(-8)-10(-3) M) concentration-dependently decreased agonist-stimulated contractile force: maximum decrease was not significantly different within the four agonists. pD(2) values for carbachol, however, were higher in atria from non-beta(1)-adrenoceptor antagonist-treated vs. beta(1)-adrenoceptor antagonist-treated patients.We conclude that, in isolated human right atria, carbachol-induced indirect negative inotropic effect is not dependent from the agonist employed to increase (via cyclic AMP accumulation) contractile force. However, in atria from beta(1)-adrenoceptor antagonist-treated patients, carbachol-induced indirect negative inotropic effect is attenuated.     

Selective degeneration of septal and hippocampal GABAergic neurons in a mouse model of amyloidosis and tauopathy

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by brain accumulation of amyloid-β peptide and neurofibrillary tangles, which are believed to initiate a pathological cascade that results in progressive impairment of cognitive functions and eventual neuronal death. To obtain a mouse model displaying the typical AD histopathology of amyloidosis and tauopathy, we generated a triple-transgenic mouse line (TauPS2APP) by overexpressing human mutations of the amyloid precursor protein, presenilin2 and tau genes. Stereological analysis of TauPS2APP mice revealed significant neurodegeneration of GABAergic septo-hippocampal projection neurons as well as their target cells, the GABAergic hippocampal interneurons. In contrast, the cholinergic medial septum neurons remained unaffected. Moreover, the degeneration of hippocampal GABAergic interneurons was dependent on the hippocampal subfield and interneuronal subtype investigated, whereby the dentate gyrus and the NPY-positive interneurons, respectively, were most strongly affected. Neurodegeneration was also accompanied by a change in the mRNA expression of markers for inhibitory interneurons. In line with the loss of inhibitory neurons, we observed functional changes in TauPS2APP mice relative to WT mice, with strongly enhanced long-term potentiation in the medial-perforant pathway input to the dentate gyrus, and stereotypic hyperactivity. Our data indicate that inhibitory neurons are the targets of neurodegeneration in a mouse model of amyloidosis and tauopathy, thus pointing to a possible role of the inhibitory network in the pathophysiological and functional cascade of Alzheimer's disease.     

ATP/IL‐33‐triggered hyperactivation of mast cells results in an amplified production of pro‐inflammatory cytokines and eicosanoids

IL‐33 and ATP are alarmins, which are released upon damage of cellular barriers or are actively secreted upon cell stress. Due to high‐density expression of the IL‐33 receptor T1/ST2 (IL‐33R), and the ATP receptor P2X7, mast cells (MCs) are one of the first highly sensitive sentinels recognizing released IL‐33 or ATP in damaged peripheral tissues. Whereas IL‐33 induces the MyD88‐dependent activation of the TAK1‐IKK2‐NF‐κB signalling, ATP induces the Ca²⁺‐dependent activation of NFAT. Thereby, each signal alone only induces a moderate production of pro‐inflammatory cytokines and lipid mediators (LMs). However, MCs, which simultaneously sense (co‐sensing) IL‐33 and ATP, display an enhanced and prolonged activation of the TAK1‐IKK2‐NF‐κB signalling pathway. This resulted in a massive production of pro‐inflammatory cytokines such as IL‐2, IL‐4, IL‐6 and GM‐CSF as well as of arachidonic acid‐derived cyclooxygenase (COX)‐mediated pro‐inflammatory prostaglandins (PGs) and thromboxanes (TXs), hallmarks of strong MC activation. Collectively, these data show that co‐sensing of ATP and IL‐33 results in hyperactivation of MCs, which resembles to MC activation induced by IgE‐mediated crosslinking of the FcεRI. Therefore, the IL‐33/IL‐33R and/or the ATP/P2X7 signalling axis are attractive targets for therapeutical intervention of diseases associated with the loss of integrity of cellular barriers such as allergic and infectious respiratory reactions.     

Discontinuing antiepileptic drugs in long-standing idiopathic generalised epilepsy

Journal of Neurology - Once adults with long-standing idiopathic generalised epilepsy have achieved stable seizure remission, patients or physicians may attempt to discontinue their antiepileptic...