Chondrocytes, the only cell type that produces cartilage, occupy a unique bioelectrical environment. Mechanical load generates bioelectrical stimulation through rapid changes in ionic and water content around cells. A chondrocytes response to changing ionic gradients plays an essential role in regulation of extra cellular matrix synthesis. An abnormal response by the cell may result in abnormal deposition of proteins leading to degeneration of tissue with pathological consequences. Typically, response to ionic and osmotic gradients across cell membranes is by ion movement through channels as a cell reacts to maintain equilibrium. Chondrocytes possess an array of ion channels on par with electrically excitable tissues, yet chondrocyte electrophysiology is much understudied. Ion channel presence in chondrocytes is now becoming apparent, however, extensive studies in human chondrocytes and how potential channel defects relate to disease are understudied. This proposal will quantify in real time dielectric properties of the membrane and cytoplasm in response to electrochemical changes to cells related to ion channel gene expression. We hypothesize that dielectric response of chondrocytes to changes in environment will be dependent upon ion channel activity. The objectives of this proposal are (1) to document dielectric changes in chondrocytes in real time when exposed to changes in osmolality, pH and ion flow using a novel microfluidic device. (2) Measure gene expression of ion channels in chondrocytes as a response to these changes. (3) Chondrocytes function under hypoxic conditions. We will directly compare dielectric response under normal versus hypoxic conditions and identify ion channels active in chondrocytes under hypoxic conditions. To our knowledge, our results will be the first description of dielectric properties of chondrocytes measured in real time and correlated to ion channel expression under hypoxia and will fundamentally impact cartilage biology unifying biomechanical and bioelectrical events in cartilage through ion channel response.

Public Health Relevance

To respond to their bioelectric and hypoxic milieu, chondrocytes possess an array of ion channels on par with electrically excitable tissues, yet chondrocyte electrophysiology is much understudied. We propose a novel and promising experimental approach where findings will have significant importance in chondrocyte electrophysiology, yet with more general applications, 1) hypoxia is a major killer, our findings will reveal in more detail how cells function under hypoxic conditions and 2) ion channels are major drug targets, and identified activity in chondrocytes will open new avenues of therapeutic intervention. This proposed study will be the first real time investigation of dielectric propertie of chondrocytes as they respond to changing physiological conditions and we expect to yield exciting and significant novel findings directly related to human health issues.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Exploratory/Developmental Grants (R21)
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Skeletal Biology Structure and Regeneration Study Section (SBSR)
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Tyree, Bernadette
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Old Dominion University
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United States
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Stacey, Michael W; Sabuncu, Ahmet C; Beskok, Ali (2014) Dielectric characterization of costal cartilage chondrocytes. Biochim Biophys Acta 1840:146-52