In the mammalian nervous system, a variety of voltage-gated potassium (K+) channels with distinct time- and voltage-dependent properties and pharmacological sensitivities have been identified. This heterogeneity has a physiological significance in that the various K+ channels function to control resting membrane potentials, action potential waveforms, repetitive firing patterns and the responses to synaptic inputs. The cloning of voltage-gated K+ channel (Ky) pore-forming (cc) and accessory (B, KChAPs, KChIPs) subunits has revealed even greater potential for generating K+ channel diversity than was expected, and the relationships between these subunits and the K+ channels in mammalian neurons is poorly understood. Here, we propose to exploit molecular genetic strategies to identify the molecular correlates of the voltage-gated K+ currents, 'Al' IAs, 'K' and ISS, in sympathetic neurons isolated from the (rat) superior cervical ganglion (SCG), and to define the functional roles of IAF, 'As' 'K' and ISS. Initial experiments will test the hypothesis that there are two molecularly distinct types of IAf channels (encoded by Kv1 and Kv4 a subunits) and determine the functional consequences of removing all IAf channels on the firing properties of SCG cells. Experiments in aims 2 and 3 will test the hypotheses that Ky alpha subunits of the Kv2 and Kv3 subfamilies underlie 'IK and IAs' respectively, in SCG neurons and define the roles 'K and IAs in shaping action potential waveforms and repetitive firing in these cells.
The final aim will explore the role(s) of the accessory KChIP proteins in the generation of functional voltage-gated K+ channels in SCG neurons. We anticipate that the studies outlined in this proposal will provide fundamentally important new insights into the molecular basis of functional voltage-gated K+ channel diversity in mammalian sympathetic neurons and into the roles of these K+ channels in the regulation neuronal excitability. Importantly, it seems likely that the multifaceted experimental approach developed here can also be applied to determine the molecular compositions and functional roles of voltage-gated (and other) K+ channels in other cells.
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