High membrane tension or loss of membrane potential causes Cch1-mediated calcium influx. (A) GCaMP-expressing cells (LGY36, MTY5, MTY21, MTY69) were exposed in a microfluidics chamber to a hypoosmotic shock (1 M sorbitol > 0 M sorbitol), and the changes in GCaMP fluorescence were monitored with time-lapse imaging. The red arrow marks the start of cell expansion for all experiments. (B) In a microfluidics chamber, cells expressing GCaMP were treated with a medium containing 40 mM Tris pH8 (resulting pH∼7.5), and the GCaMP signal was monitored by time-lapse imaging. (C) Change in cell surface area caused by the addition of 40 mM Tris pH8 (LGY36, MTY21). The box-and-whisker plots indicate the mean.