The arterial baroreceptors are sensory endings restricted to the carotid sinus and aortic arch but with powerful regulatory influences. They transduce arterial pressure signals into neurohumoral regulation of cardiovascular structure and homeostasis. Despite a large amount of information on the determinants of activation of baroreceptor (BR) nerves, the molecular, cellular and functional determinants of mechanoelectrical transduction at their sensory nerve endings are largely unknown. Project IV of this PPG addresses the neurobiology of mechanosensation. This Project (IV.A.1) which was initiated four years ago, as focused on 1) the identification of BR neurons in the nodose ganglion; 2) culturing them in vitro; 3) the development of a quantitative system for their mechanical activation; and 4) the definition of their responses with measurements of whole cell membrane currents, single-channel openings [Ca2+]i. A functional correlate of the cellular mechanisms was sought by measurements of carotid sinus nerve activity in vivo. Based on very exciting preliminary studies, we now propose to test the hypothesis that the ENaC/degenerin family of proteins represent ionic channel responsible for mechanoelectrical transduction in BR neurons. This hypothesis gains a strong rationale from the discovery of a genetic link between touch sensation in C. Elegans and the evidence of mechanical activation of ENaC/degenerin channels. In preliminary studies we found that 1) the subunits of ENAC/degenerin, gamma ENaC; beta ENaC and BNC1 (recently cloned from brain), are expressed in the aortic arch adventitia in the nodose ganglia where the BR nerve terminals and BR neurons are located, respectively; 2) the activity of BNC1a (transfected into oocytes) is blocked by Gd3+, a known blocker of mechanosensory channels; and 3) the rise in [Ca2+]i in BR neurons during mechanical stimulation is blocked by amiloride, a known blocker of the ENaC/degenerin channels.
Our aims are: first, to identify ENaC/degenerin ENaC/degenerin channels; and third, to attempt to disrupt the BR responses to mechanical stimulation at the cellular, organ and whole animal level by transfection of dominant- negatives of ENaC/degenerin family. The uniqueness of the project is in the joining of two leading laboratories, with expertise in neurobiology of autonomic control (Abboud) and in the molecular biology of ion channels (Welsh). With the added support of excellent cores in imaging, transgenic animals, and gene transfer, the promise of successful pursuit of this problem is ascertained.
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