Figure 7.

Loss of Ca²⁺ dependence of the LIC in Asp⁶²¹ mutants. A, B, In wild-type (trpl) (A) and trp^D621E (B), responses to brief (1 ms) flashes in normal bath (1.5 mm Ca²⁺) activated and deactivated rapidly. During perfusion with a Ca²⁺-free solution, responses were reduced in amplitude and both on- and off-kinetics greatly slowed. C, In trp^D621G, responses were slow under both conditions and showed virtually no differences in amplitude or kinetics. D, Normalized, averaged responses from wild-type photoreceptors recorded in Ca²⁺-free solution and trp^D621G recorded in the presence of 1.5 mm Ca²⁺ were indistinguishable. E, Summary of kinetics data: time-to-peak and time-to-decay to 25% of peak response (t25%). In wild-type and trp^D621E flies, both time-to-peak and time-to-decay to 25% of peak response slowed substantially in Ca²⁺-free solution. In trp^D621G, there was no significant dependence on extracellular Ca²⁺, and response kinetics were statistically indistinguishable from wild type.