The presence of TASK-3 channels has been described in a number of healthy and malignantly transformed cells, showing mainly intracellular distribution with relatively insignificant labelling of the cell surface membrane. In this work, immunochemical and molecular biology methods were utilised to establish the intracellular organelle whose TASK-3 expression accounts for this strong intracellular labelling using cultured melanoma and HaCaT cells. Before the immunocytochemical experiments, the presence of TASK-3 mRNA was also confirmed in melanoma cells. Comparison of the results of the TASK-3- and mitochondrion-specific labelling indicated that the TASK-3 channel subunits were strongly expressed by mitochondria in both investigated cell types. Moreover, prominent TASK-3 expression of keratinocytes could also be demonstrated in histological sections excised from the human skin. These results indicate that TASK-3 channels are present in the mitochondria in both malignantly transformed and healthy cells, suggesting that they might have roles in ensuring mitochondrial functions.

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.

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-Bihar Megyei Kené zy Gyula County Infirmary, Debrecen, Hungary (Á P) S U M M A R Y Because the neuronal membrane properties and firing characteristics are crucially affected by the depolarization-activated K 1 channel (Kv) subunits, data about the Kv distribution may provide useful information regarding the functionality of the neurons situated in the cochlear nucleus (CN). Using immunohistochemistry in free-floating slices, the distribution of seven Kv subunits was described in the rat CN. Positive labeling was observed for Kv1.1, 1.2, 1.6, 3.1, 3.4, 4.2, and 4.3 subunits. Giant and octopus neurons showed particularly strong immunopositivity for Kv3.1; octopus neurons showed intense Kv1.1-and 1.2-specific reactions also. In the latter case, an age-dependent change of the expression pattern was also documented; although both young and older animals produced definite labeling for Kv1.2, the intensity of the reaction increased in older animals and was accompanied with the translocation of the Kv1.2 subunits to the cell surface membrane. The granule cell layer exhibited strong Kv4.2-specific immunopositivity, and markedly Kv4.2-positive glomerular synapses were also seen. It was found that neither giant nor pyramidal cells were uniform in terms of their Kv expression patterns. Our data provide new information about the Kv expression of the CN and also suggest potential functional heterogeneity of the giant and pyramidal cells. (J Histochem Cytochem 56:443-465, 2008) K E Y W O R D S hearing rhodamine immunohistochemistry confocal microscopy age dependence glomerular synapse THE MAMMALIAN cochlear nucleus (CN) is an assembly point of numerous types of neurons forming local networks that receive and process the primary acoustic information arriving from the cochlea (Brawer et al. 1974;Disterhoft et al. 1980;Webster and Trune 1982;Hackney et al. 1990). The nucleus is divided into three morphologically distinct parts (anteroventral, posteroventral, and dorsal divisions; aVCN, pVCN, and DCN, respectively), each contacted by the incoming and branching axons of the auditory nerve (Moore 1986). Because of the fact that these regions of the CN play different roles in the processing of the auditory information, the parallel secondary pathways emerging from the CN and targeting higher centers in the brain carry activity patterns, providing information about different features of the sound (Cant and Benson 2003; Malmierca 2003).To understand the function of the CN, it is essential to know how the various cell types contribute to its overall task. Thus far, numerous authors have provided valuable information about the morphological and functional properties of the individual CN neurons, revealing that the behavior and firing characteristics of the projection cells of the CN are markedly different. The bushy neurons (Brawer et al. 1974) of the VCN produce rapidly adapting (type II) response pattern [i.e., they fire a single action potential at the start of suprathreshold electrical stimulation (Manis and Marx 1991;Schwarz an...

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