Meeting Abstract

P3.141  Monday, Jan. 6 15:30  Cardiac muscle in Homarus americanus responds differently to loading in transverse and longitudinal directions DICKINSON, E.*; JOHNSON, A.S.; ELLERS, O.; DICKINSON, P.S.; Bowdoin College; Bowdoin College; Bowdoin College; Bowdoin College edickins@bowdoin.edu

Central pattern generators (CPGs) are neural networks that generate stereotyped outputs, which drive rhythmic behaviors. CPGs can be modulated by neurotransmitters and feedback systems; in Homarus americanus, the neurogenic heart is controlled by a CPG: the cardiac ganglion, which generates bursts of action potentials that drive cardiac contractions. There are over 80 different identified neurotransmitters in the lobster; however, the effects of the stretch feedback system on CPG are less well understood. Since the heart is naturally loaded in three dimensions by pressure, uniaxial and biaxial (longitudinal and transverse) stretches of 2.5 mm were imposed on the heart muscle to understand the effects of stretch in cardiac modulation. The active force (force of contraction) increased in response to both transverse and longitudinal uniaxial stretching; however, the increase in force of contraction was greatest under transverse loading. The passive forces increased in response to both transverse and longitudinal uniaxial stretching, but longitudinal loading resulted in the greatest increase. Transverse but not longitudinal uniaxial loading had a state-dependent effect on frequency. Biaxial loading increased both the force of contraction and the passive forces during stretch and additionally had a state-dependent effect on frequency. These initial results suggest that the different muscle characteristics in the longitudinal and transverse direction, in conjunction with the stretch that occurs during normal cardiac function, is important in determining overall contraction parameters in the heart. Supported by NSF Grant IOS-1121973, and NIH Grants 5P20RR016463-12 and 8P20GM103423-12.