BKβ1 Subunits Contribute to BK Channel Diversity in Rat Hypothalamic Neurons

Large conductance Ca(2+)-activated BK channels are important regulators of action potential duration and firing frequency in many neurons. As the pore-forming subunits of BK channels are encoded by a single gene, channel diversity is mainly generated by alternative splicing and interaction with auxiliary beta-subunits (BK beta 1-4). In hypothalamic neurons several BK channel subtypes have been described electrophysiologically; however, the distribution of BK beta subunits is unknown so far. Therefore, an antibody against the large extracellular loop of the BK beta 1 subunit was raised, freed from cross-reactivity against BK beta 2-4 and affinity-purified. The resulting polyclonal monospecific BK beta 1 antibody was characterized by Western blot analysis, ELISA techniques and immunocytochemical staining of BK beta 1-4-transfected CHO and COS-1 cells. Regional and cellular distribution in the rat hypothalamus was analysed by immunocytochemistry and in situ hybridization experiments. Immunocytochemical staining of rat hypothalamic neurons indicates strong BK beta 1 expression in the supraoptic nucleus and the magno- and parvocellular parts of the paraventricular nucleus. Lower expression was found in periventricular nucleus, the arcuate nucleus and in the median eminence. Immunostaining was predominantly localized to somata. In addition, pericytes and ependymal epithelial cells showed BK beta 1 labelling. In all cases immunocytochemical results were supported by in situ hybridization.