Prolonged calcium influx after termination of light-induced calcium release in invertebrate photoreceptors
MetadataShow full item record
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, influx through light-activated ion channels contributes to the Ca2+ increase. In contrast, in other species, such as Lima, Ca2+ is initially only released from an intracellular pool, as the light-sensitive conductance is negligibly permeable to calcium ions. As a consequence, coping with sustained stimulation poses a challenge, requiring an alternative pathway for further calcium mobilization. We observed that after bright or prolonged illumination, the receptor potential of Lima photoreceptors is followed by the gradual development of an after-depolarization that decays in 1–4 minutes. Under voltage clamp, a graded, slow inward current (Islow) can be reproducibly elicited by flashes that saturate the photocurrent, and can reach a peak amplitude in excess of 200 pA. Islow obtains after replacing extracellular Na+ with Li+, guanidinium, or N-methyl-D-glucamine, indicating that it does not reflect the activation of an electrogenic Na/Ca exchange mechanism. An increase in membrane conductance accompanies the slow current. Islow is impervious to anion replacements and can be measured with extracellular Ca2+ as the sole permeant species; Ba can substitute for Ca2+ but Mg2+ cannot. A persistent Ca2+ elevation parallels Islow, when no further internal release takes place. Thus, this slow current could contribute to sustained Ca2+ mobilization and the concomitant regulation of the phototransduction machinery. Although reminiscent of the classical store depletion–operated calcium influx described in other cells, Islow appears to diverge in some significant aspects, such as its large size and insensitivity to SKF96365 and lanthanum; therefore, it may reflect an alternative mechanism for prolonged increase of cytosolic calcium in photoreceptors.
© The Authors, 2009 . 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 134 (2009): 177-189, doi:10.1085/jgp.200910214.
The following license files are associated with this item:
Except where otherwise noted, this item's license is described as Attribution-NonCommercial-ShareAlike 3.0 United States
Showing items related by title, author, creator and subject.
Ross, William N. (2012-01)All cells use changes in intracellular calcium concentration [Ca2+]i to regulate cell signaling events In neurons, with their elaborate dendritic and axonal arborizations, there are clear examples of both localized and ...
Voltage-gated calcium channel subunits from platyhelminths : potential role in praziquantel action Jeziorski, Michael C.; Greenberg, Robert M. (2006-02-07)Voltage-gated calcium (Ca2+) channels provide the pathway for Ca2+ influxes that underlie Ca2+-dependent responses in muscles, nerves, and other excitable cells. They are also targets of a wide variety of drugs and toxins. ...
Dendritic signals from rat hippocampal CA1 pyramidal neurons during coincident pre- and post-synaptic activity : a combined voltage- and calcium-imaging study Canepari, Marco; Djurisic, Maja; Zecevic, Dejan (2006-11-16)The non-linear and spatially inhomogeneous interactions of dendritic membrane potential signals that represent the first step in the induction of activity dependent long-term synaptic plasticity are not fully understood, ...