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Signals from cone photoreceptors to L‐type horizontal cells are differentially modulated by low calcium in carp retina
Author(s) -
Xu HongPing,
Luo DongGen,
Yang XiongLi
Publication year - 2001
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.0953-816x.2001.01515.x
Subject(s) - retina , neuroscience , carp , cone (formal languages) , biology , physics , anatomy , biophysics , fish <actinopterygii> , computer science , algorithm , fishery
Ca 2+ plays crucial roles in both phototransduction and calcium‐dependent glutamate release from the photoreceptor terminal. Modulation, by lowering extracellular Ca 2+ , of red‐sensitive (R‐) and short wavelength‐sensitive (S‐) cone‐driven light responses of L‐type horizontal cells (LHCs) was studied in the isolated superfused carp retina using intracellular recording techniques. Low Ca 2+ (nominally Ca 2+ ‐free) Ringer's reduced responses of LHCs to both green (500 nm) and red (680 nm) flashes in darkness, with the former being suppressed more substantially than the latter. This differential suppression became more significant when contribution of R‐cones to the green‐light‐induced responses was diminished by a moderate red (680 nm) background light. Application of IBMX, an inhibitor of phosphodiesterase (PDE), increased LHC responses to both red and green flashes equally, resembling the effect of low Ca 2+ on phototransduction. In addition, photopic electroretinographic P III responses, reflecting the activity of cones, to red flashes were more potentiated by low Ca 2+ , compared to those to green flashes, whilst they were both equally potentiated by IBMX. Furthermore, low Ca 2+ caused a more pronounced suppression of LHC responses to red flashes than those to green flashes in the presence of IBMX. It is postulated that reduction of LHC responses in low Ca 2+ may be due to the ‘saturation suppression’ caused by the increased glutamate release from the photoreceptor terminal and the differential modulation may reflect a consequence of the dual action of low Ca 2+ on the PDE activity in the photoreceptor outer segment and the synaptic strength between cones and LHCs.