title: Measurement of the intracellular free calcium concentration in salamander rods.
abstract: Measurement of the free calcium concentration within a photo-receptor outer segment has been considered an important aim since the proposal by Hagins and Yoshikami that the primary event in phototransduction is a release of Ca (2+) inside the cell. More recent evidence has cast doubt on the calcium hypothesis, and the observations of Yau and Nakatani and Matthews et al. suggest that the internal Ca (2+) concentration ([Ca (2+)]i), may decrease after a flash of light. In the present study we have measured [Ca (2+)]i directly by using a new method for incorporating the Ca-sensitive photoprotein aequorin into an isolated rod. We report that the light response is accompanied by a decrease in [Ca (2+)]i, caused by the closure of light-sensitive channels which are the main route for Ca (2+) entry into the outer segment. Of the Ca (2+) entering through light-sensitive channels, about 95% is sequestered by a rapid and reversible buffering mechanism. Calcium is removed from the cell by an electrogenic pump in which 3 Na (+) ions are exchanged for each Ca (2+); the pump is highly active and the free Ca (2+) in the cell declines with a time constant of ~0.5 s after a flash of light.
authors: P A
authors: PA
authors: McNaughton
authors: L
authors: L
authors: Cervetto
authors: B J
authors: BJ
authors: Nunn
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000557:Ambystoma / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000032:analysis*; D002122:Calcium Chloride / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects; D042541:Intracellular Space / Q000737:chemistry*; D008027:Light; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010775:Photic Stimulation; D017948:Retinal Rod Photoreceptor Cells / Q000737:chemistry* / Q000187:drug effects
chemical_list: D010726:Phosphodiesterase Inhibitors; D002122:Calcium Chloride; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine