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Gravity Dependent Ca⁺⁺ Signaling in Ceratopteris Measured Using a MEMS Based In-Silico Cell Electrophysiology Sensor Device.   D.M. Porterfield^1,2,3, S.J. Roux⁴, A. ul Haque^1,2, M. Salmi⁴, W.T. McLamb⁵, M. Rokkam^1,6, A.R. DeCarlo^1,2, S.T. Wereley⁷.

¹Physiological Sensing Facility, ²Dept. of Ag. & Bio. Eng., ³Dept. of Hort. & Landscape Arch., ⁴Molecular, Cell. & Dev. Biol., Univ. of Texas, Austin, TX, ⁵Dynamac Corporation, KSC, FL. ⁶Dept. of Elec. & Comp. Eng., ⁷Dept. of Mech. Eng., Purdue Univ., W. Lafayette, IN,

   Polar ion currents driven by Ca⁺⁺ have been studied in numerous developmental systems. These studies have shown that ion currents can direct polarity in cellular development, and in Ceratopteris this polar current correlates with gravity sensing. Critical questions that still need to be answered in this system require spatial and temporal resolutions that exceed that available using the self-referencing microsensor technique. We have developed an in-silico Cell Electrophysiology Lab-on-a-Chip (CEL-C) device that has enabled us to monitor Ca⁺⁺ ion currents through multiple fern spores in real time. Using an advanced physiological sensing modality, called dual electrode differential coupling, we can directly measure trans-cellular ion currents across the cell. In static ground studies we have been able to replicate earlier published reports that show Ca⁺⁺ currents through the cell correlate with gravity responsiveness. We have also been able to continuously measure Ca⁺⁺ currents in dynamic experiments where the CEL-C device and the immobilized cells are being rotated. Full 180^o rotation was done in 5 seconds and the polar current reversed to full magnitude in 20-25 seconds. Microgravity flight experiments were flow on the NASA’s reduced gravity DC-9 and allowed us to measure cellular responses as gravity changed from microgravity to 2g. The top-bottom Ca⁺⁺ current changed in phase with the accelerometer data, whereas side-side controls did not show any predictable pattern related to the reduced gravity flight. These data obtained using the CEL-C device have allowed us to analyze the dynamics involved with gravity sensing in this single cell system, at a level of resolution not previously possible.

(Supported by the NASA and the Lilly Foundation)