Figure 7.

Sr²⁺ substitution affects wt and itpr mosaics similarly. A, Substitution of control bath (1.5 Ca²⁺, 4 Mg²⁺ upper traces) with nominally Ca²⁺- and Mg²⁺-free solution and 1.5 mm Sr²⁺ without EGTA in the bath (lower traces from same cells). Left, response to 1-ms flashes containing ∼25 effective photons; right, quantum bumps in response to continuous dim light from itpr-null photoreceptor cells recorded using EGTA (1 mm) in the electrode. B, Summary of QE data from itpr-null mosaics and wild-type controls (+/+). C–F, Bath substitution with EGTA buffered Sr²⁺ (1 mm EGTA, nominally 0 Ca²⁺, 0 Mg²⁺ and 2.5 mm Sr²⁺: free [Sr²⁺] = 1.5 mm). Upper traces, before; bottom traces, same cells after perfusing with EGTA-buffered Sr²⁺ solution. C, Quantum bumps elicited under these conditions showed defects in both controls (itpr/+) and null mutants (itpr), often showing amplification only after a slow ramping phase (arrows). D, However, QE was only slightly affected, with no discernible difference between itpr and itpr/+ controls. E, Macroscopic responses to 1-ms flashes (∼25 effective photons) under the same conditions (slower traces during 0 Ca²⁺, 0 Mg²⁺ 1.5 Sr²⁺ plus EGTA perfusion). F, Peak amplitudes of responses were similarly affected in itpr and itpr/+ controls.