Phototransduction

• DARK: rod/cone membrane is DEPOLARIZED by cGMP (cyclic guanosine monophsophate)

• cGMP gates Na+ channels -- V = -40 mV

• LIGHT:photopigment in rod/cone disks absorbs photons initiates decrease in cGMP -- V = -65 mV (hyperpolarization)

• Photopigment:11-cis retinal+protein(opsin/rhodopsin) (configuration change--activate transducin--breakdown cGMP)

cGMP phosphodiesterase

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