Meeting Abstract

P2.170  Saturday, Jan. 5  The effect of regional phenotypic differences of Procambarus clarkii opener muscle on sarcomere length, fiber diameter, and force development HOLSINGER, RC*; COOPER, RL; University of Kentucky; University of Kentucky rcholsinger@uky.edu

The opener muscle in the walking legs of the crayfish (Procambarus clarkii) is innervated by only one excitatory motor neuron although there are regional differences across the muscle. The distal, central and proximal muscle fibers have varied biochemistry and physiology associated with them, including synaptic structure, presence of troponin T, EPSP amplitudes and facilitation, fiber diameter, sarcomere length, and force generation. Because the differences in synaptic structure and physiology have previously been described, here we will present how the EPSPs and force generation vary between the muscle fiber regions. Innervation of the proximal fibers produced larger excitatory postsynaptic potentials (EPSPs) than those of the central fibers with distal fibers’ EPSPs showing intermediate levels. These differences in EPSP amplitudes were correlated with differences in short-term facilitation between the three regions, as various stimulation frequencies of the excitor motor nerve produced different amounts of force in each of the regions as well as the whole muscle, with the proximal developing force most quickly. The proximal muscle fibers were also found to have the shortest sarcomeres when measured with the claw relaxed. These data support the idea that the proximal region of the opener muscle is phasic-like tissue and central is tonic-like tissue.