Store-operated channels regulate intracellular calcium in mammalian rods.
Exposure to daylight closes cyclic nucleotide-gated (CNG) and voltage-operated Ca(2+) -permeable channels in mammalian rods. The consequent lowering of the cytosolic calcium concentration ([Ca(2+)](i)), if protracted, can contribute to light-induced damage and apoptosis in these cells. We here report that mouse rods are protected against prolonged lowering of [Ca(2+)](i) by store-operated Ca(2+) entry (SOCE). Ca(2+) stores were depleted in Ca(2+)-free saline supplemented with the endoplasmic reticulum (ER) sequestration blocker cyclopiazonic acid. Store depletion elicited [Ca(2+)](i) signals that exceeded baseline [Ca(2+)](i) by 5.9 ± 0.7-fold and were antagonized by an inhibitory cocktail containing 2-APB, SKF 96365 and Gd(3+). Cation influx through SOCE channels was sufficient to elicit a secondary activation of L-type voltage-operated Ca2+ entry. We also found that TRPC1, the type 1 canonical mammalian homologue of the Drosophila photoreceptor TRP channel, is predominantly expressed within the outer nuclear layer of the retina. Rod loss in Pde6b(rdl) (rd1), Chx10/Kip1(-/-rdl) and Elovl4(TG2) dystrophic models was associated with ∼70% reduction in Trpc1 mRNA content whereas Trpc1 mRNA levels in rodless cone-full Nrl(-/-) retinas were decreased by ∼50%. Genetic ablation of TRPC1 channels, however, had no effect on SOCE, the sensitivity of the rod phototransduction cascade or synaptic transmission at rod and cone synapses. Thus, we localized two new mechanisms, SOCE and TRPC1, to mammalian rods and characterized the contribution of SOCE to Ca(2+) homeostasis. By preventing the cytosolic [Ca(2+)](i) from dropping too low under sustained saturating light conditions, these signalling pathways may protect Ca(2+)-dependent mechanisms within the ER and the cytosol without affecting normal rod function.
Department of Ophthalmology & Visual Sciences, Moran Eye Center, University of Utah School of Medicine, Salt Lake City, UT 84132, USA.
Tünde
T
Molnar
Peter
P
Barabas
Lutz
L
Birnbaumer
Claudio
C
Punzo
Vladimir
V
Kefalov
David
D
Križaj
D000818:Animals; D050976:Basic-Leucine Zipper Transcription Factors / Q000172:deficiency / Q000235:genetics; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology*; D005136:Eye Proteins / Q000235:genetics; D006706:Homeostasis; D008027:Light; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D018345:Mice, Knockout; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology; D050052:TRPC Cation Channels / Q000502:physiology*
D050976:Basic-Leucine Zipper Transcription Factors; D015220:Calcium Channels; D005136:Eye Proteins; C084884:Nrl protein, mouse; D050052:TRPC Cation Channels; C104603:TRPC3 cation channel; C096351:transient receptor potential cation channel, subfamily C, member 1; D002118:Calcium