The calcium and voltage regulated BK(or SLO1)-type K+ channel is a widely expressed ion channel impacting on regulation of excitability in a variety of both excitable and inexcitable tissues. SLO1 is encoded by the kcnma1(or slo1) gene, which was the first discovered member of the SLO family of four distinct homologous genes. Other SLO family members include the pH-regulated SLO3 channel, expressed exclusively in mammalian sperm and two K+ channels regulated primarily by cytosolic Na+, SLO2.1 and SLO2.2. The ability of SLO family channels to be regulated by cytosolic ions is mediated by the large cytosolic regulatory domain, containing specific ion binding sites, that is connected to the pore-forming part of the subunits. The ability of SLO family channels to respond to changes in the cytosolic milieu makes them uniquely adapted to play negative feedback roles following activity that leads to alterations in the cytosolic ions. In addition to their regulation by cytosolic ligands, an important component of SLO channel function is their regulation by associated auxiliary subunits. For BK channels, despite being encoded by only a single gene, important functional diversity arises from tissue- specific expression of up to four different auxiliary ? subunits (?1-?4) and a newly identified family of ? subunits. ???and ?4 subunits have been implicated in hypertension and epilepsy, respectively, and other indications suggest that BK channels may be therapeutic targets in stroke, hypertension, epilepsy, and tumor growth regulation. Of auxiliary subunits, little is known about the locations of expression and physiological roles of ?2 and ?3 subunits, and even less is known about ? subunits. This lab uses methods spanning biophysical analysis through whole- animal physiological and behavioral analysis to assess not only topics pertinent to the biophysical and functional properties of channels of different auxiliary subunit composition but also how these channels contribute to electrical excitability in native cells. To probe physiological function in native cells, we utilize genetic knock-out (KO) of specific regulatory channel subunits. Recently, this lab presented the initial work on a ?2 KO mouse, and future work will present similar examinations of other regulatory subunits. Such KO models are particular advantageous for providing clues about whether abnormal aspects of channel function or expression may underlie particular disease pathologies. This project is expected to provide new insight into the physiological roles of ?2, ?3 and ?1 auxiliary subunits, and the roles of BK channels containing such subunits.
Four highly homologous genes of the SLO family encode potassium channel pore-forming subunits that are broadly expressed among tissues, share the feature that they are regulated by dynamic changes in specific cytosolic ion concentrations, and broadly influence function and electrical excitability in cells in which they are found. Diversity in function of such channels arises from tissue-specific expression of two families of auxiliary subunits (? and ?), which in some cases have been implicated in various pathologies linked to specific SLO family channels, such as hypertension and epilepsy. Using methods of electrophysiology coupled with genetic manipulations that delete specific subunits from mice, this project is part of a long-term effort to clearly define the functional properties conferred on SLO family channels by their auxiliary subunits, how channels of a specific subunit composition impact on cellular physiology, and whether such channels may underlie any pathological changes in cell physiology.
