Prolonged depolarization in rods in situ

Abstract

Intracellular recordings were made from rods in the superfused retina of the marine toad (Bufo marinus). It was found that injection of a brief depolarizing current pulse (0.04-1 nA) evoked a distinctive, long-lasting response, here called "the prolonged depolarization." The response appears to be regenerative, has a stereotypical waveform, is typically about 6 mV in amplitude and 3 s in duration, and has a relatively long recovery period (10-60 s). As a rule, the response cannot be directly evoked by light but the current-evoked response is significantly enhanced in the presence of steady illumination. The light-evoked hyperpolarization and the depolarizing spikes of the rod are both attenuated in the presence of the prolonged depolarization. The prolonged depolarization is not an altered manifestation of the depolarizing spikes of toad rods since both can be recorded simultaneously and steady illumination suppresses the spikes while enhancing the prolonged depolarization. The response is enhanced in chloride-free superfusate and also appears to be enhanced by the use of electrodes containing chloride. The response is markedly shortened in superfusates that lack calcium or contain 1-5 mM cobalt. On this and other evidence, it is suggested that the response may be generated by the sequential action of calcium channels and calcium-activated chloride channels. Although rarely evoked by light, the prolonged depolarization of toad rods is otherwise remarkably similar to the prolonged depolarization of turtle cones. It is proposed that the prolonged depolarization, in contrast to the feedback depolarization of cones, arises from mechanisms common to both rods and cones.

Lateral interactions in the outer retina

“…Burkhardt et al (1988) showed evidence for three components in the surround responses of turtle cones: 1) an initial graded depolarization, 2) spikes, and 3) long regenerative events that lasted for many seconds and were termed “prolonged depolarizations.” Subsequent work showed that prolonged depolarizations are triggered by the regenerative activation of L-type Ca 2+ channels and exhibit a long-lasting plateau phase maintained by the activation of Ca 2+ -activated Cl − channels (Thoreson and Burkhardt, 1991; Barnes and Deschenes 1992). Prolonged depolarizing responses with similar waveforms have been observed in cones and rods from a number of species (turtle cones: Burkhardt et al, 1988; Cervetto and Piccolino, 1982; salamander cones: Lasansky, 1981; toad rods: Burkhardt et al, 1991; mouse rods: Babai and Thoreson, 2009). …”

Photoreceptor encoding of supersaturating light stimuli in salamander retina

“…Regenerative potentials have been recorded in rods during the recovery phase of the light response when the retina was treated with TEA to block potassium channels (Fain & Quandt, 1980; Fain et al 1980). A prolonged depolarization was also observed in rods after injection of brief depolarizing current pulses in cells with high internal chloride (Thoreson & Burkhardt, 1991; Burkhardt et al 1991). In 20% of cones in turtle retina, feedback from horizontal cells evokes a spike (Piccolino & Gerschenfeld, 1980).…”

Calcium-induced calcium release contributes to synaptic release from mouse rod photoreceptors

“…In two rods, we observed large, prolonged depolarizing responses with waveforms similar to prolonged depolarizing responses found in rods and cones of other species (Burkhardt et al . 1988, 1991; Thoreson & Burkhardt, 1991; Barnes & Deschenes, 1992). These earlier studies showed that prolonged depolarizing responses begin when an initial small depolarization (e.g., due to activation of Ca 2+ -activated Cl − channels by CICR) stimulates the regenerative activation of voltage-gated Ca 2+ channels.…”