UBC Theses and Dissertations
Single channel properties of the slow cardiac potassium current, IKs Werry, Daniel
The slow potassium current, IKs, abbreviates the cardiac action potential by repolarizing the membrane to a resting state. Mutations in the pore-forming IKs subunit, KCNQ1, cause long QT syndrome type 1 (LQT1), which increases risk of fatal arrhythmia. Despite the physiological and clinical importance of IKs, little is known about the elementary events that underlie the unique biophysical properties of the channel, and how these elementary events are altered in the face of disease. This thesis investigates single channel recordings of IKs with and without mutations that cause LQT1 using patch clamp electrophysiology. Single channel IKs is described by slow and fast gating processes. The channel is slow to open, but flickers rapidly between open and closed states in non-deactivating bursts. Long latency periods to opening underlie the slow activation of IKs at depolarized potentials. Channel activity is cyclic with periods of high activity followed by quiescence, leading to an overall low open probability. The mean single channel conductance was determined to be 3.2 pS and long-lived subconductance levels coupled to activation were observed. Single channel properties of IKs with LQT1 mutations in the S3 helix of the voltage sensing domain in KCNQ1 were investigated to uncover pathogenic mechanisms at the single molecule level. Open probability was reduced in loss-of-function mutations (D202H, I204F and V205M) and increased in a unique gain-of-function mutation (S209F) that may cause LQTS from a reduced number of functional channels at the cell surface. The mean duration of open events correlated well with deactivation rate in all mutants and first latency to opening determined activation rate. From these results, we attributed the pathogenic mechanisms of LQT1 mutations to alterations in the stability of specific channel states.
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