Fig. 9.

Light-induced Ca²⁺ signals measured in the absence of extracellular Ca²⁺. Substantial Ca²⁺ increases were detected in every cell in response to saturating UV-measuring stimuli: Ca²⁺ signals (upper traces), simultaneously recorded whole-cell currents at 0 and −70 mV (lower traces) (two different cells). The rise was at least as large in cells clamped at 0 mV as in those clamped at −70 mV, arguing against influx of residual Ca²⁺ as an explanation. Note also that the initial (dark) resting level of Ca²⁺ was higher in the cell clamped at 0 mV (see also Fig. 11). Bath contained 0 Ca²⁺, 2 mm EGTA, and 120 mmNaCl.