6 BK Channels – Focus on Polyamines, Ethanol/Acetaldehyde and Hydrogen Sulfide (H 2 S) Anton Hermann 1 , Guzel F. Sitdikova 2 and Thomas M. Weiger 1 1 University of Salzburg, Department of Cell Biology, Division of Cellular and Molecular Neurobiology, Salzburg 2 Kazan Federal University, Department Physiology of Man and Animals, Kazan 1 Austria 2 Russia 1. Introduction Calcium (Ca 2+ )-activated potassium (K + ) channels are activated by the synergistic action of voltage as well as by Ca 2+ which links these channels to cell metabolism. Because of their high level of functional diversity the channels are widely expressed in a remarkable amount of different cells from bacteria to men and found in a great variety of tissues such as sensory, muscle, vascular or the brain. The channels are among the most frequently studied K + channels giving rise to an impressive amount of knowledge about their structure and function. The idea of a Ca 2+ -activated conductance was born in 1958 during studies on erythrocytes by Gardos (1958) who showed that metabolically deprived cells in the presence of internal Ca 2+ augment the permeability of the cell plasma membrane to K + ions. The finding was further elaborated by direct injection of Ca 2+ ions into mollusc neurons (Meech & Standen 1975; Gorman & Hermann 1979) which supported the idea of a Ca 2+ - and voltage dependent membrane K + conductance and showed that it is also present in excitable cells. Up to present Ca 2+ -activated K + conductances were and still are studied in great detail concerning their biophysical, physiological, pathophysiological, pharmacological, structural and functional properties (for early and recent reviews see Meech 1978; Hermann & Hartung 1983; Latorre et al.. 1989; Kaczorowski et al. 1996; Gribkoff, et al. 2001; Jiang et al., 2001; Weiger et al. 2002; Calderone 2002; Jiang et al., 2002) Maher & Kuchel 2003; Salkoff et al. 2006; Pluznick & Sansom 2006; Cui et al. 2009; Wu et al. 2010; Lee & Cui 2010; Grimm & Sansom 2010; Hill et al. 2010; Berkefeld et al. 2010; Cui 2010). In the first sections of this chapter after we briefly describe techniques to record BK channels we review some properties of BK channels which appeared important in the context of our further presentations. Ethanol is produced by the cell metabolism and is generally known as one of the most ancient and most ubiquitous psychoactive drugs consumed by humans. There are myriads of publications on the effects of alcohol on body functions, behavior, social interactions or