Figure 11.

Effect of intracellular dialysis with BAPTA. (A) Photoreceptor cells were stimulated with flashes of increasing intensity in the dark-adapted state (D) or in the presence of a steady background illumination (L). The two families of recordings on the left were obtained with the standard internal solution containing 1 mM EGTA; the ones on the right were obtained with 10 mM BAPTA in the patch pipette. In both conditions the background light compressed the amplitude range of the response (calibration bars: left, 200 ms/200 pA; right, 200 ms/100 pA). The corresponding plots of the peak response amplitude as a function of the log of test light attenuation show that in both conditions the background light caused a similar reduction of the saturating flash response (80–85%), and a nearly identical shift of the light intensity eliciting a half-maximal photocurrent (Δσ = 0.73 log). (B) Normalized half saturating responses measured in the dark-adapted and the light-adapted state. Both the control and the BAPTA-treated photoreceptor exhibit a pronounced acceleration of the photoresponse kinetics in the presence of the background light. Test flashes were 100 ms in duration; unattenuated intensity: 11 × 10¹⁶ photons · cm⁻² · s⁻¹. Background light intensity: 5.3 × 10¹⁴ photons · cm⁻² · s⁻¹. Holding potential: −20 mV; cells superfused with standard ASW.