Investigating Prolonged Depolarizing Afterpotential (PDA) in Drosophila Photoreceptors

Secure a white-eyed Drosophila fly to a holder in a recording arena. 

Position a light source near the fly.

Implant the ground electrode into the fly's back.

Insert the recording electrode into the outer periphery of the fly's eye, near the retinal photoreceptor cells containing a photopigment.

Dark-adapt the fly briefly. This converts metarhodopsin, the light-activated form of the photopigment, to rhodopsin, its inactive form.

Apply a high-intensity orange light pulse. This converts any remaining metarhodopsin to rhodopsin.

Next, apply blue light pulses. The blue light converts rhodopsin to metarhodopsin, initiating a signaling cascade and opening specific ion channels.

This induces a continuous positive ion influx and sustained depolarization, even after the blue light is removed — the prolonged depolarizing afterpotential, or PDA, recorded by the electrode.

Now, reapply the orange light pulses to convert the metarhodopsin to rhodopsin.

This stops the signaling cascade, terminates the PDA, and repolarizes the photoreceptor membrane.