Effects of Sodium, Potassium, and Calcium Ions on Slow and Spike Potentials in Single Photoreceptor Cells

Abstract

The influence of changes in the ionic composition of the bathing medium on responses of the retinula cell of the honeybee drone to light was examined by means of intraceUular microelectrodes. The resting potential of the cell was influenced mainly by the concentration of K. The peak of the receptor potential (the transient), which in a normal solution and with strong light approaches zero membrane potential, overshot this level in a K-rich solution. An increase in the concentration of K also raised the level of the steady-state phase of the receptor potential (the plateau). The amplitude of the receptor potential was decreased and the spike potential rapidly abolished when Na was replaced by either sucrose, choline, or Tris. In a Ca-free solution the amplitude of the response and especially that of the plateau, was increased. An increase in Ca had the opposite effects. All these changes were reversible. An attempt was made to interpret the receptor and spike potentials in terms of passive movements of Na and K across the membrane of the retinnla cell. The major difficulty encountered was to find an explanation for the persistence of an appreciable fraction of the transient and the plateau in preparations kept up to 12 hr in a solution in which all the Na had been replaced by choline, Tris, or sucrose.

Voltage‐activated potassium channels in blowfly photoreceptors and their role in light adaptation.

“…Although there are a number of reports of potassium conductances in arthropod photoreceptors (bee: Fulpius & Baumann, 1969;barnacle: Hanani & Shaw 1977;locust: Tsukahara 1980), only in Limulus has a delayed rectifier current been clearly implicated (Pepose & Lisman, 1978;review by Fain & Lisman, 1981). The delayed rectifier in Limulus differs considerably from that in the fly in its kinetics, its voltage activation range (threshold ca -40 mV, cf.…”

“…These mechanisms, and their functional significance, have been most extensively described in Limulus ventral photoreceptors (Pepose & Lisman, 1978; O'Day, Lisman & Goldring, 1982; review by Fain & Lisman, 1981) where both a delayed rectifier and an 'A' current participate in light adaptation by reducing light-induced voltages. In other arthropods, however, the available evidence only indicates the existence of calcium-activated potassium conductances (bee : Fulpius & Baumann, 1969;barnacle: Hanani & Shaw, 1977; fly: Muijser, 1979;Weckstr6m, 1989;locust: Tsukahara, 1980). In molluscan photoreceptors the situation appears more complex with voltage-sensitive calcium currents, calciumactivated potassium currents, delayed rectifiers and 'A' currents all having been reported in the same cells (Alkon, Sakakibara, Froman, Harrigan, Lederhendler & Farley, 1985;Nasi, 1991).…”

Intrinsic noise in locust photoreceptors.

“…Bumps and larger receptor potentials are produced as a result of an increase in membrane conductance to ions, principally sodium, whose electrochemical gradient favours depolarization (review: Meech & Brown, 1976;Fulpius & Baumann, 1969). We assume that variations in bump amplitude are due to an underlying variability in the number of conductance channels activated by a single photon absorption, and that the ratio between the mean number of activated channels and the variance remains constant at all intensities.…”

Two Light-Induced Processes in the Photoreceptor Cells of Limulus Ventral Eye

“…Photoreceptor cells in many arthropods respond to light with a change in membrane voltage, the receptor potential; the amplitude of this receptor potential is graded with the intensity of the light (Hartline et al, 1952;Tomita 1956;Naka, 1961;Eguchi, 1965;Fulpius and Baumann, 1969). In the eyes of two such arthropods (the barnacle, Balanus sp.…”