Received: 19 April 2017 Revised: 28 July 2017 Accepted: 3 August 2017 DOI: 10.1002/jez.2096 RESEARCH ARTICLE The effects of potassium and muscle homogenate on proprioceptive responses in crayfish and crab Cole Malloy 1 Viresh Dayaram 1 Sarah Martha 1,2 Brenda Alvarez 1 Ikenna Chukwudolue 1 Nadera Dabbain 1 Dlovan D. mahmood 1 Slavina Goleva 1 Tori Hickey 1 Angel Ho 1 Molly King 1 Paige Kington 1 Matthew Mattingly 1 Samuel Potter 1 Landon Simpson 1 Amanda Spence 1 Henry Uradu 1 Jacob Van Doorn 1 Kristin Weineck 3 Robin L. Cooper 1 1 Department of Biology, University of Kentucky, Lexington, Kentucky 2 College of Nursing, University of Kentucky, Lexington, Kentucky 3 Department of Medicine, Rostock University, Rostock, MV, Germany Correspondence Robin L. Cooper, Department of Biology, Univer- sity of Kentucky, Lexington, KY 40506-0225. Email: RLCOOP1@uky.edu Funding information Contract grant sponsor: University of Ken- tucky; Neurophysiology Lab (Bio446, Bio650); Deutscher Akademischer Austausch Dienst (DAAD) German Academic Exchange Service; Research Internships in Science and Engineering (RISE - Program). Many of the authors were students in a neu- rophysiology lab-based class who addressed authentic scientific-based questions in regards to the topic of examining how extra- and intra- cellular pH would influence proprioception. This course project is part of a new trend in teach- ing science to undergraduates (Linn, Palmer, Baranger, Gerard, & Stone, 2015). Course- based undergraduate research experiences (CUREs) are relatively new and an approach being adopted by science educators in high schools and colleges(Bakshi, Patrick, & Wis- chusen, 2016). Abstract Proprioception of limbs and joints is a basic sensory function throughout most of the animal kingdom. It is important to understand how proprioceptive organs and the associated sensory neurons function with altered environments such as increased potassium ion concentrations ([K + ]) from diseased states, ionic imbalances, and damaged tissues. These factors can drastically alter neuronal activity. To assess this matter, we used the chordotonal organ in a walking leg of a blue crab (Callinectes sapidus) and the muscle receptor organ of the crayfish (Procambarus clarkii). These organs serve as tractable models for the analysis of proprioception. The prepara- tions can help serve as translational models for these effects, which may be observed in other invertebrate species as well as mammalian species (including humans). When extracellular potassium concentration ([K + ] o ) is increased to 20 mM in both preparations, mixed results are observed with activity increasing in some preparations and decreasing in others after mechanical displacement. However, when [K + ] o is increased to 40 mM, activity drastically decreases in all preparations. Additionally, proprioceptor sensory activity declines upon exposure to a diluted muscle homogenate, which contains a host of intracellular constituents. The robust effects of altered [K + ] on proprioception in these models illuminate the potential detriments on neuronal function in cases of severe tissue damage as well as altered [K + ] o . 1 INTRODUCTION The treatment of tissue injury by health care providers is complex depending on the type of injury, tissue type, and location. Treat- ment and care for healing goes beyond focusing on the injured site itself since other body systems and healthy tissue can be indirectly affected (Brancaccio, Lippi, & Maffulli, 2010; Cintra-Francischinelli et al., 2010). This is particularly an issue with large amounts of tissue injury due to the spillage of intracellular constituents into extracellular fluid (ECF) and entrance into the blood stream or into the hemolymph in the case of invertebrates. Compartmentation of dense tissue can reduce the effect to the rest of the body but may have an increased effect on the neighboring cells within the compartment. The acute and long-term effects on healthy tissue, which is exposed to cellular debris, are varied. The initial tramatome can have a mild to large effect on surrounding tissue depending on the amount of tissue initially damaged, degree of compartmentation, amount of ionic spillage, carbon dioxide (CO 2 ) accumulation, and resultant J. Exp. Zool. 2017;327:366–379. c  2017 Wiley Periodicals, Inc. 366 wileyonlinelibrary.com/journal/jez