Ultraviolet-Induced Sensitivity to Visible Light in Ultraviolet Receptors of Limulus

Abstract

In the UV-sensitive photoreceptors of the median ocellus (UV cells), prolonged depolarizing afterpotentials are seen following a bright UV stimulus. These afterpotentials are abolished by long-wavelength light. During a bright UV stimulus, long-wavelength light elicits a sustained negative-going response. These responses to long-wavelength light are called repolarizing responses. The spectral sensitivity curve for the repolarizing responses peaks at 480 nm; it is the only spectral sensitivity curve for a median ocellus electrical response known to peak at 480 nm. The reversal potentials of the repolarizing response and the depolarizing receptor potential are the same, and change in the same way when the external sodium ion concentration is reduced. We propose that the generation of repolarizing responses involves a thermally stable intermediate of the UV-sensitive photopigment of UV cells.

Pigment transformation and electrical responses in retinula cells of drone, Apis mellifera male.

“…This feature has been demonstrated in arthropods (Wald & Hubbard, 1957;Brown & Brown, 1958;Hubbard & St George, 1958) and in insects (Hamdorf et al 1968;Gogala, Hamdorf & Schwemer, 1970;Razmjoo & Hamdorf, 1976), and some attempts have been made to correlate spectral properties of the different states of the pigments with electrical responses to light (Nolte & Brown, 1972a, b;Minke, Hochstein & Hillman, 1973;Hochstein et al 1973;Tsukahara & Horridge, 1977). Nolte & Brown (1972b) proposed, for the Limul8 median eye, that photoconversion of the U.V. pigment from its primary state (VP 360) into a stable photoproduct (M 480) induces a prolonged depolarizing afterpotential (PDA), while the reverse conversion in darkness is responsible for the slow return of the membrane potential to its resting level.…”

Two light-dependent conductances in Lima rhabdomeric photoreceptors.

“…Under certain conditions, a long-lasting tail (called prolonged depolarizing afterpotential, or PDA) has been observed in the photoresponse of many invertebrate visual cells, such as the UV-sensitive photoreceptors of the median ocellus of Limulus (Nolte and Brown, 1972), and the photoreceptors ofBalanus (Hochstein et al, 1973). This phenomenon appears to be related to the presence of long-lived photoproducts of rhodopsin, and can be induced by intense stimulation causing a net shift in pigment state (when the absorption spectra of the photopigment and that of the photoproduct are different), but not by spectrally "neutral" stimuli (for a comprehensive review, see Hillman et al, 1983).…”

“…This phenomenon appears to be related to the presence of long-lived photoproducts of rhodopsin, and can be induced by intense stimulation causing a net shift in pigment state (when the absorption spectra of the photopigment and that of the photoproduct are different), but not by spectrally "neutral" stimuli (for a comprehensive review, see Hillman et al, 1983). The membrane conductance changes underlying the PDA are apparently the same as those responsible for the late receptor potential (Nolte and Brown, 1972;Hochstein et al, 1973;Brown and Cornwall, 1975), and can last for extended periods of time (tens of seconds to hours). While in this report no attempt was made to investigate wavelength-dependent effects, the second component of the photocurrent of Lima ceils does not share many similarities with the PDA: (a) the late wave can be elicited by white light, which should be a neutral stimulus in a cell not previously subjected to chromatic adaptation; (b) its duration is only on the order of a few hundred milliseconds; and (c) the underlying ionic mechanisms are clearly different from those of the early phase of the light response.…”

Rapid photopigment conversions in blowfly visual sense cells consequences for receptor potential and pupillary response

“…The present consensus is that rhodopsin photosensitivity is the only determinant for the spectral sensitivity of the dark adapted cell at low light intensities (Goldsmith, 1972;Atzmon et al, 1978;Strong and Lisman, 1978). High light intensities of a selected wavelength range eliciting a high rhodopsin conversion rate versus little metarhodopsin conversion result in prolonged depolarizing afterpotentials (PDA); wavelengths inducing a high metarhodopsin conversion rate annihilate the PDA (barnacle: Hochstein et al, 1973;blowfly: Hamdorf and Razmjoo, 1977;Muijser et al, 1975;dronefly: Tsukahara et al, 1977;Limulus: Nolte and Brown, 1972;Minke et al, 1973). Related electrophysiological phenomena expressing visual pigment conversions are the fast photovoltages or early receptor potentials (ERP; barnacle: Hillman et al, 1973;Minke et al, 1973Minke et al, , 1974Minke et al, , 1978 Limulus: Lisman and Sheline, 1976;Lisman and Bering, 1977;fly: Pak and Lidington, 1974;Kirschfeld et al, 1977;Stark et al, 1977).…”