On the gating mechanisms of the light-dependent conductance in Pecten hyperpolarizing photoreceptors : does light remove inactivation in voltage-dependent K channels?
Gomez, Maria del Pilar
MetadataShow full item record
KeywordPhotoreceptors; CNG channel; Potassium ion channels; Gating, ion channels; Blockers, potassium channel
The hyperpolarizing receptor potential of ciliary photoreceptors of scallop and other mollusks is mediated by a cGMP-activated K conductance; these cells also express a transient potassium current triggered by depolarization. During steady illumination, the outward currents elicited by voltage steps lose their decay kinetics. One interesting conjecture that has been proposed is that the currents triggered by light and by depolarization are mediated by the same population of channels, and that illumination evokes the receptor potential by removing their steady-state inactivation. Exploiting the information that has become available on the phototransduction cascade of ciliary photoreceptors, we demonstrated that the same downstream signaling elements are implicated in the modulation of voltage-elicited currents: direct chemical stimulation both at the level of the G protein and of the final messenger that controls the light-dependent channels (cGMP) also attenuate the falling phase of the voltage-activated current. Application of a protein kinase G antagonist was ineffective, suggesting that a cGMP-initiated phosphorylation step is not implicated. To ascertain the commonality of ionic pathways we used pharmacological blockers. Although millimolar 4-aminopyridine (4-AP) suppressed both currents, at micromolar concentrations only the photocurrent was blocked. Conversely, barium completely and reversibly antagonized the transient voltage-activated current with no detectable effect on the light-evoked current. These results rule out that the same ionic pores mediate both currents; the mechanism of light modulation of the depolarization-evoked K current was elucidated as a time-dependent increase in the light-sensitive conductance that is superimposed on the inactivating K current.
© 2005 Gomez et al. This article is distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License. The definitive version was published in Journal of General Physiology 125 (2005): 455-464, doi:10.1085/jgp.200509269.
The following license files are associated with this item:
Except where otherwise noted, this item's license is described as http://creativecommons.org/licenses/by-nc-sa/3.0/
Showing items related by title, author, creator and subject.
Prolonged calcium influx after termination of light-induced calcium release in invertebrate photoreceptors Gomez, Maria del Pilar; Nasi, Enrico (Rockefeller University Press, 2009-08-31)In microvillar photoreceptors, light stimulates the phospholipase C cascade and triggers an elevation of cytosolic Ca2+ that is essential for the regulation of both visual excitation and sensory adaptation. In some organisms, ...
Melanopsin-expressing amphioxus photoreceptors transduce light via a phospholipase C signaling cascade Angueyra, Juan Manuel; Pulido, Camila; Malagon, Gerardo; Nasi, Enrico; Gomez, Maria del Pilar (Public Library of Science, 2012-01-03)Melanopsin, the receptor molecule that underlies light sensitivity in mammalian ‘circadian’ receptors, is homologous to invertebrate rhodopsins and has been proposed to operate via a similar signaling pathway. Its downstream ...
Dissecting the determinants of light sensitivity in amphioxus microvillar photoreceptors : possible evolutionary implications for melanopsin signaling Ferrer, Camilo; Malagon, Gerardo; Gomez, Maria del Pilar; Nasi, Enrico (Society for Neuroscience, 2012-12-12)Melanopsin, a photopigment related to the rhodopsin of microvillar photoreceptors of invertebrates, evolved in vertebrates to subserve nonvisual light-sensing functions, such as the pupillary reflex and entrainment of ...