Application of ion-sensitive field effect transistors for ion channel screening

Cell-based screening assays are now widely used for identifying compounds that serve as ion channel modulators. However, instrumentation for the automated, real-time analysis of ion flux from clonal and primary cells is lacking. This study describes the initial development of an ion-sensitive field effect transistor (ISFET)-based screening assay for the acquisition of K+ efflux data from cells cultured in multi-well plates. Silicon-based K+-sensitive ISFETs were tested for their electrical response to varying concentrations of KCl and were found to display a linear response relationship to KCl in the range of 10 µM-1 mM. The ISFETs, along with reference electrodes, were inserted into fast-flow chambers containing either human colonic T84 epithelial cells or U251-MG glioma cells. Application of the Ca2+ ionophore A23187 (1 µM), to activate Ca2+-activated non-selective cation (NSC) channels (T84 cells) and large conductance Ca2+-activated K+ (BK) channels (U251 cells), resulted in time-dependent increases in the extracellular K+ concentration ([K+]o) as measured with the ISFETs. Treatment of the cells with blockers of either the NSC or BK channels, caused a strong inhibition of the A23187-induced increase in [K+]o. These results were consistent with ion current measurements obtained using the whole-cell arrangement of the patch clamp procedure. In addition, K+ efflux data could be acquired in parallel from multiple cell chambers using the ISFET sensors. Given the non-invasive properties of the probes, the ISFET-based assay should be adaptable for screening ion channels in various cell types.