RESUMEN
Although cholinergic modulation of the cochlear nucleus (CN) is functionally important, neither its cellular consequences nor the types of receptors conveying it are precisely known. The aim of this work was to characterise the cholinergic effects on giant cells of the CN, using electrophysiology and quantitative polymerase chain reaction. Application of the cholinergic agonist carbachol increased the spontaneous activity of the giant cells; which was partly the consequence of the reduction in a K(+) conductance. This effect was mediated via M4 and M3 receptors. Cholinergic modulation also affected the synaptic transmission targeting the giant cells. Excitatory synaptic currents evoked by the stimulation of the superficial and deep regions of the CN were sensitive to cholinergic modulation: the amplitude of the first postsynaptic current was reduced, and the short-term depression was also altered. These changes were mediated via M3 receptors alone and via the combination of M4, M2 and M3 receptors, when the superficial and deep layers, respectively, were activated. Inhibitory synaptic currents evoked from the superficial layer showed short-term depression, but they were unaffected by carbachol. In contrast, inhibitory currents triggered by the activation of the deep parts exhibited no significant short-term depression, but they were highly sensitive to cholinergic activation, which was mediated via M3 receptors. Our results indicate that pre- and postsynaptic muscarinic receptors mediate cholinergic modulation on giant cells. The present findings shed light on the cellular mechanisms of a tonic cholinergic modulation in the CN, which may become particularly important in evoking contralateral excitatory responses under certain pathological conditions.
Asunto(s)
Núcleo Coclear/metabolismo , Neuronas/metabolismo , Receptores Muscarínicos/metabolismo , Animales , Carbacol/farmacología , Colinérgicos/farmacología , Núcleo Coclear/efectos de los fármacos , Núcleo Coclear/fisiología , Electrofisiología , Femenino , Potenciales Postsinápticos Inhibidores/efectos de los fármacos , Potenciales Postsinápticos Inhibidores/fisiología , Masculino , Neuronas/efectos de los fármacos , Neuronas/fisiología , Técnicas de Cultivo de Órganos , Ratas , Ratas Wistar , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
Although the hyperpolarization-activated non-specific cationic current (I(h)) plays important roles in determining the membrane characteristics of the spiral ganglion cells (SGCs), neither the exact types of the hyperpolarization-activated, cyclic nucleotide-gated, cation non-selective channel (HCN) subunits contributing to the molecular assembly of the relevant channels, nor their distribution pattern presented by the SGCs is known. In the present work immunolabeling and Western blot analysis were performed to describe the presence and distribution of all four known HCN subunits in the guinea-pig spiral ganglion. Besides determining the expression of the HCN1-HCN4 subunits by both type I and type II SGCs, the presence of possible apico-basal gradients in the expression patterns was also sought. The results indicate that both type I and type II SGCs express all four HCN subunits. The intensity of the immunolabeling of the cell surface membrane was generally strong, but it showed pronounced cell-to-cell variability. The Western blot experiments in combination with densitometry revealed that the amount of the HCN1 and HCN3 proteins was more significant in the apical than in the basal third of the guinea-pig cochlea. These findings not only imply potential heteromeric HCN channel formation of the spiral ganglion neurons, but they also offer a possible explanation of the previously reported heterogeneity of I(h) recorded in functional studies.
Asunto(s)
Canales Catiónicos Regulados por Nucleótidos Cíclicos/metabolismo , Expresión Génica/fisiología , Neuronas/metabolismo , Subunidades de Proteína/metabolismo , Ganglio Espiral de la Cóclea/citología , Animales , Canales Catiónicos Regulados por Nucleótidos Cíclicos/clasificación , Canales Catiónicos Regulados por Nucleótidos Cíclicos/genética , Cobayas , MasculinoRESUMEN
Amplification of the kcnk9 gene and overexpression of the encoded channel protein (TASK-3) seems to be involved in carcinogenesis. In the present work, TASK-3 expression of melanoma cells has been studied. For the investigation of TASK-3-specific immunolabelling, a monoclonal antibody has been developed and applied along with two, commercially available polyclonal antibodies targeting different epitopes of the channel protein. Both primary and metastatic melanoma cells proved to be TASK-3 positive, showing prominent intracellular TASK-3-specific labelling; mostly concentrating around or in the proximity of the nuclei. The immunoreaction was associated with the nuclear envelope, and with the processes of the cells and it was also present in the cell surface membrane. Specificity of the immunolabelling was confirmed by Western blot and transfection experiments. As TASK-3 immunopositivity of benign melanocytes could also be demonstrated, the presence or absence of TASK-3 channels cannot differentiate between malignant and non-malignant melanocytic tumours.