Mf. Cuttle et al., DIURNAL MODULATION OF PHOTORECEPTOR POTASSIUM CONDUCTANCE IN THE LOCUST, Journal of comparative physiology. A, Sensory, neural, and behavioral physiology, 176(3), 1995, pp. 307-316
Single electrode clamp techniques demonstrated diurnal changes in phot
oreceptor membrane conductance, recorded intracellularly in the intact
, dark-adapted retina of the locust Schistocerca gregaria. In the day,
locust photoreceptors exhibited the membrane properties of fast cells
, as previously defined in rapidly moving diurnal Diptera. Depolarizat
ion activated a powerful potassium conductance with two kinetic compon
ents, one rapidly activating close to resting potential and the other
activating more slowly when further depolarized, giving a pronounced d
elayed rectification. There was little inactivation. At night, locust
photoreceptors resembled slow cells, as defined in weakly flying crepu
scular and nocturnal Diptera. Depolarization rapidly activated an outw
ard current which then inactivated over 100 ms to reduce rectification
. The change from day to night state was mimicked by applying 10 mM se
rotonin extracellularly to the retina. We conclude that the potassium
conductances of locust photoreceptor membranes are modulated according
to a diurnal rhythm, possibly by serotonin. This neuromodulation is u
sed to match photoreceptor membrane properties to photic habitat. Our
findings suggest a definite and potentially widespread function for se
rotonin as a mediator of diurnal changes in the insect visual system.