Electrical impulses generated by nerve, skeletal muscle, and heart muscle cells play an essential role in coordination of most physiological functions and in information processing, learning and memory in the central nervous system. Electrical signals are transmitted from cell to cell by synaptic transmission. Research in this laboratory is focused on the voltage-gated sodium and calcium channels which are responsible for action potential generation in nerve and muscle and for initiation of synaptic transmission. We study the structure and function of these ion channels, their regulation by physiological pathways, drugs, and neurotoxins, and their role in coordination of electrical excitability and synaptic transmission in neurons.
Purified channel proteins, cloned DNA probes which encode the structure of these ion channels, site-directed mutagenesis and functional expression, and site-directed antibodies which recognize specific peptide segments are used to probe the molecular mechanisms of ion channel function, biosynthesis, assembly, and localization. The sodium channel beta subunits have been found to serve as both modulators of channel activity and cell adhesion molecules which may determine channel localization. Specific protein segments of the pore-forming alpha subunits which form the voltage sensors and inactivation gate of the sodium channel have been defined and their functional roles determined by mutagenesis and biophysical analysis. The three-dimensional structure of the inactivation gate of the sodium channel has been determined by NMR methods and correlated with its physiological function.
Regulation of ion channel properties by physiological stimuli is of great interest as a potential mechanism of information processing, learning, and memory in the central nervous system. Sites of phosphorylation by specific protein kinases and sites of binding of G protein subunits which modulate sodium and calcium channel function have been identified. A novel A Kinase Anchoring Protein which targets cAMP-dependent protein kinase to sodium and calcium channels has been discovered and characterized at the molecular and functional levels. In addition, a synaptic protein interaction (synprint) site through which presynaptic calcium channels interact with the SNARE proteins involved in transmitter release has been identified and shown to play a critical role in synaptic transmission and in calcium channel regulation.
Clinically important drugs, including local anesthetics, antiarrhythmics, antiepileptics, and calcium antagonists alter the properties of voltage-sensitive ion channels. We are currently investigating the sites and mechanisms by which these drugs alter the properties of ion channels in order to define the mechanism of drug action at the molecular level and identify common themes which may be important in development of new therapeutic agents. Recent work has led to the identification of the receptor sites for the calcium antagonist drugs on calcium channels and the receptor sites for local anesthetic drugs and multiple neurotoxins on sodium channels.