Figure 2. Two-electrode recordings allow pharmacological manipulation of cone phototransduction.

a. Phototransduction cascade. Light-activated Opsin activates transducin (Gt), which then activates phosphodiesterase (PDE). Active PDE reduces the cyclic-GMP (cGMP) concentration, closing membrane channels. Cyclic-GMP is restored by guanylate cyclase (GC).

b. Changes in holding current before (black) and after (gray) introduction of a second electrode; both electrodes contained control internal solution. Filled black and gray circles represent 500 ms stretches of noise used to calculate the spectra in (d).

c. Light responses and noise before (black) and after (gray) introduction of the second electrode (time points noted in (b)). Upper left shows expanded examples of noise used to calculate the power spectra in (d).

d. Power spectra before (black circles) and after (gray circles) the introduction of the second electrode.

e. Average (± SEM, n=16) ratio between power spectra calculated before and after introduction of the second electrode.

f. Omission of both ATP and GTP from the internal solution shuts down the phototransduction cascade, causing cGMP-gated channels to close.

g. Changes in holding current during a two-electrode recording in which both electrodes contained a solution lacking ATP and GTP. Filled black and purple circles represent 500 ms stretches of noise used to calculate the spectra in (i).

h. Examples of light responses and noise recorded before (black) and after (purple) the introduction of a second electrode (time points noted in (g)).

i. Power spectra before (black) and after (purple) the introduction of the second electrode.

j. Average (± SEM, n=6) ratio of power spectra before and after the introduction of the second electrode. Conditions as in (g).