Figure 4. Vertical motions induced by cis-MAM at the I328C/S345C mutant increase ATP function.
(A) Normalized whole-cell currents evoked by a saturating concentration of ATP (100 μM) recorded before (gray trace) and after (black trace) treatment with MAM. Inset highlights part of the currents upon ATP washout, fitted to single exponential decay functions (red traces). (B) Whole-cell light-gated currents recorded from the same cell in the presence (left) or absence (right) of ATP (100 μM). Gray trace indicates the predicted current if ATP-gated and light-gated currents at 365 nm were additive. (C) Concentration–response relationships for ATP at 525 nm (open circle, trans state) or in the dark immediately after illumination at 365 nm (filled triangle, cis state) (n = 4–8 cells; mean ± s.e.m.). Currents were normalized to 100 μM ATP at 365 nm and 300 μM ATP at 525 nm. The Hill equation was fit to the data.