| In this thesis I will begin by describing the cloning and characterization of three of the mammalian members of the SK family of K+ channels. These channels regulate processes that range from secretion of salt and water by epithelial cells to neuronal firing patterns to the immune response of T-cells to a foreign antigen. I will argue that my data support a mechanism of inhibition of at least one type of SK channel by charybdotoxin that shares some fundamental similarities with mechanisms of block of BK and voltage-gated channels but that differs somewhat in the details of the interaction between toxin and channel. In addition, I will present evidence that Ba2+, which is generally thought to occlude the pores of K+ channels, may bind within a unique, membrane-delimited cavity within SK channels. I will show that at depolarized potentials Ba2+ appears to be pushed out of this cavity and into the deep pores of at least two types of SK channels where it blocks permeation of K+ ions. I will also demonstrate that calmodulin is likely to mediate both gating and assembly of SK channels. Finally, I will describe the cloning, expression, and characterization of a distantly related member of the BK family of K+ channels called Slack. BK channels regulate action potential duration and synaptic transmission, smooth muscle contractility and vasodilation, and endocrine and exocrine secretion, among other important physiological processes. I will show that when expressed heterologously, the product of the Slack gene generates outwardly-rectifying, K+-selective currents. The selective expression of Slack in brain and kidney coincides with some of the tissues in which the original BK gene, Slo, was found to be expressed. I will present evidence that when coexpressed, Slack and Slo appear to coassemble to generate Ca2+-activated K+ channels of intermediate conductance. |
