FIGURE 3.

Concentration-dependent saturable activation of ORA1 by 4-hydroxyphenylacetic acid. HEK 293T cells transfected with ORA1 or empty vector were stimulated with different concentrations of 4-hydroxyphenylacetic acid, and calcium responses were imaged. For each concentration an average trace of three identically treated wells is shown (left panel). No response is seen for ORA1-transfected cells stimulated with buffer and for empty vector-transfected cells in all conditions (bottom panels). Note that ORA1-transfected cells are at least 10-fold more sensitive to 4-hydroxyphenylacetic acid than to aged tyrosine. Scale bar: y axis, arbitrary units; x axis, 2 min.