Meeting Abstract

P3.185  Monday, Jan. 6 15:30  Mechanisms and effects of stretch feedback in the lobster heart HARMON, K*; CHIN-PURCELL, M; DICKINSON, PS; Bowdoin College pdickins@bowdoin.edu

The neurogenic heart of the lobster, Homarus americanus, is controlled by a small pattern generator, the cardiac ganglion (CG). Previous studies suggest that crustacean heart muscle provides feedback to the CG, and that this may be mediated by stretch sensitive dendrites projecting from the CG neurons themselves. We thus wished to determine whether this is the case in the lobster, and whether the effects of stretch as well as the mechanisms that underlie stretch sensitivity are the same in lobsters as in the crab and isopod species in which stretch has previously been examined. When the lobster heart was stretched tonically, contraction frequency increased significantly in approximately 89% of animals; it decreased in 7% and remained unchanged in 4%. Severing the putative stretch-sensitive dendrites that branch from the main trunk of the ganglion decreased or eliminated the response to stretch in 75% of preparations, suggesting that these processes are a major source of stretch sensitivity. To determine the cellular mechanism that underlies stretch sensitivity, we recorded intracellularly from CG motor neurons while stretching small bundles of muscle fibers. Stretch of a single muscle bundle did not alter cycle frequency, and we saw no change in membrane potential between bursts. Surprisingly, the amplitude of the driver potentials that underlie bursting in these neurons decreased when the muscles were stretched. Both the changes in heartbeat frequency in response to removal of the dendrites and the responses of the membrane potential to stretch differ considerably from those previously recorded in other species. Supported by NSF Grant IOS-1121973, NIH Grants 5P20RR016463-12 (NCRR) and 8P20GM103423-12 (NIGMS), and the Paller Fund of Bowdoin College.