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1Author    Hennig Stieve, Gabriele Rüsing, Weijia Yuan, H.Thomas HennigRequires cookie*
 Title    The Effects of Externally Applied Lithium and Strontium on the Arsenazo-Monitored Cytosolic Calcium Signal of the Limulus Ventral Photoreceptor  
 Abstract    The intracellular arsenazo signal indicating the transient light-evoked change in cytosolic Ca2+ (or Sr2+) concentration was measured in Lim ulus ventral photoreceptor simultaneously with the receptor potential at 15 °C. The decline of the arsenazo signal has two phases (D 1 and D 2) when the photoreceptor is bathed in physiological saline. 1. When calcium is replaced by strontium in the superfusate both receptor potential and arsenazo signal are markedly increased in amplitude and the membrane potential is hyper­ polarized. The decline of the arsenazo signal is prolonged and becom es monophasic; the fast phase D 1 of the decline disappears. 2. In strontium saline under voltage clamp conditions the slope o f the monophasic decline of the arsenazo signal is the steeper the more negative the membrane voltage. 3. After replacing sodium by lithium in the superfusate the rise of the receptor potential and of the arsenazo signal are not much altered. The decline of the arsenazo signal, however, is slowed down more than 3-fold; this is due to the complete suppression of the fast phase D1 and the retardation o f the slow phase D 2 of the calcium re-decline. Interpretation: 1. The N a -C a exchanger can accept strontium as a calcium substitute. Strontium has a weaker desensitizing action than calcium. Strontium is not -or only very little -taken up by the endoplasmic cisternae. 2. In sodium-free lithium saline the N a -C a exchanger, the N a -K ATPase and the calcium uptake system of the endoplasmic cisternae do not function. Therefore the intracellular calcium level rises. Abbreviations: Arsenazo III, 2,2'-(l,8-dihydroxy-3,6-di-sulfo-2-naphthalene-bis(azo)dibenzenearsonic acid; AS, arsenazo signal; cGMP, guanosine 3':5'-cyclic m ono­ phosphate; D l , D 2 , fast and slow phase o f decline of the arsenazo signal; EGTA, ethylene glycol-bis(ß-aminoethylether)-N,N,N',N'-tetraacetic acid; calcium chelating agent; F, area, time integral of light-evoked sig­ nal; Hmax, peak height of a light-evoked signal; IP3, ino­ sitol 1,4,5-trisphosphate; Mi, initial slope, mean slope of rise from end of latency until half height o f the signal; Mm, median slope of rise, slope of rise at half height of the signal; PMP, prestimulus membrane potential; PS, physiological saline; ReP, receptor potential, light-evoked membrane voltage signal; SRC, subrhabdomeric cisternae; Tlat, latency, time from stimulus onset to first significant start of the response; Tmax, time-to-peak from stimulus onset; Tr, rise time (Tmax -Tlat); T2, decay time, time during which the response decays from its maximum to 50% of that value. 
  Reference    Z. Naturforsch. 49c, 372 (1994); received March 14 1994 
  Published    1994 
  Keywords    Limulus Photoreceptor, R eceptor Potential, Intracellular Arsenazo Signal, Cytosolic Calcium or Strontium Transient, Lithium 
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 TEI-XML for    default:Reihe_C/49/ZNC-1994-49c-0372.pdf 
 Identifier    ZNC-1994-49c-0372 
 Volume    49