Cell reactions to dielectrophoretic manipulation

The phenomenon of dielectrophoretic particle manipulation holds promise for many biotechnology applications, including cell sorting. In our system cel l manipulation normally involves transient exposure (15 minutes) to radio-f requency AC electric fields generated using planar microelectrodes. The pre sent study was designed to investigate the range of acute effects of dielec trophoretic manipulation on the normal physiology of isolated cells. Cells were suspended in isoosmotic Mannitol and exposed to a 5 MHz, 21 V (peak to peak) electric field with 100 mu m gap electrodes. Cells were assigned to three experimental groups; non-exposed controls, exposed cells processed im mediately after cessation of the field, and exposed cells processed after a time delay. SEM: observations of spread cells cultured on the devices show ed no apparent acute effects of field exposure on cell morphology. Cell-dou bling rates in exposed cells subsequent to field-exposure or transient incu bation in mannitol were no different from control cells. An MTT 'mitochondr ial stress' assay indicated no alteration in the rate of oxidative respirat ion in exposed cells 0.5 hour after exposure to the field. Western blot ana lysis indicated upregulation of fos protein in cells 0.5 hour after field-e xposure, which was confirmed using densitometry, Reverse transcription of c ellular mRNA followed by PCR amplification, polyacrylamide gel electrophore sis and autoradiography of cDNA banding revealed differential gene expressi on between controls and exposed cells processed immediately after cessation of the field. Differential gene expression persisted in exposed cells at l east 0.5 hours after removal from the field. Observations indicated that te mperature fluctuation in the mannitol solution was minimal, suggesting that upregulated mRNA may not have been related to thermally-induced heat shock protein, The present study has indicated that exposure to AC fields during dielectrophoretic cell manipulation is associated with upregulation of the intermediate-early gene cfos and also transcription of other as yet uniden tified genes. These transcriptional events were not manifest as gross chang es in cell morphology or cell-cycle dynamics. (C) 1999 Academic Press.