Potassium channels are protein-lined pores that span the lipid bilayer and act essentially as highly selective enzymes that catalyse the movement of potassium ions across the cell membrane. Potassium ion movement across the membrane tends to drive the membrane voltage toward the equilibrium potential for potassium (~ -90 mV), consequently these channels play a vital role in determining cell excitability and, by extension, cell function. For example, ATP-gated potassium channels play a role in coupling the increase of plasma glucose to insulin secretion; voltage-gated potassium channels affect the rhythm of the heart and influence chemical signalling between neurones in the brain.
From the many types of K channels that exist we have chosen to focus on voltage-gated K+ channels. In this class of channel the probability that the channel is open and conducting is determined by the membrane voltage. Using the voltage clamp technique we address questions such as the voltage-dependence of activation, the mechanism(s) of inactivation, the ionic selectivity of the channel pore and the influence of test substances on channel behaviour. Recently, the focus in the lab has shifted from potassioum channels expressed in pituitary cells (melanotrophs), to cloned channels. In this approach, and in collaboration with Dr. Fedida’s lab, molecular biological techniques are used to express normal and point-mutated K+ channels in a cell line (human embryonic kidney (HEK) cells) so that recording from a homogeneous population of channels is facilitated. Ultimately, by examining the effects of organic substances and ions (e.g. Zn2+, H+) on the behaviour of normal and mutant channels we hope to develop our understanding of structure/function relationships in these wonderfully interesting proteins.
Students who study in the lab may expect to learn voltage clamp recording of macroscopic and microscopic (single channel) currents using patch electrodes, the use of computers for data analysis and modelling of current behaviour and, finally, the application of molecular biology in the expression of wild-type and mutated potassium channels.