Islow is not solely controlled by store depletion. (A) Application of 400 nM thapsigargin in the dark by local superfusion (indicated by the horizontal line beneath the trace) only produced a very small change in membrane current. Holding potential of 50 mV. (B) Islow evoked in a thapsigargin-treated cell has a normal amplitude and time course. (Inset) Photocurrent measured in response to bright flashes, showing that the light response is greatly attenuated. (C) Effect of thapsigargin on light-evoked calcium mobilization. Cells were loaded with 83 µM Oregon Green2 by dialysis. Compared with the pronounced increase in Ca fluorescence consistently recorded in control cells (left traces), in thapsigargin-treated cells (400 nM) the calcium transient is either abolished or dramatically attenuated (right). (D) Average light-induced increase in Ca fluorescence for three control cells and three cells exposed to thapsigargin. Error bars indicate SEM.
