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1997 (1)
1994 (1)
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 
2Author    Georg Stommel, Gabriele Rüsing, Weijia Yuan, Hennig StieveRequires cookie*
 Title    Cytosolic Calcium Transient and Light Response in Limulus Ventral Nerve Photoreceptors: Supralinearity in Response-Intensity Curves  
 Abstract    Light-evoked intracellular electrical responses were measured simultaneously with the changes in intracellular free Ca2+ or Sr2+ concentration by means of arsenazo III. The re-sponse-versus-stimulus intensity characteristics was measured in two states of relative light adaptation in strontium-containing saline (10 mM Sr2+; 0.25 mM Ca2+). Supralinear parts of the curves with slopes > 1 were found for the receptor current amplitude and the current­ time integral as well as for the amplitude of the arsenazo signal within at least 0.3 log units of identical stimulus intensity range. Maximum slopes of response-versus-intensity curves are on average approximately 1.7 for the receptor current and the arsenazo signal in both adaptational states. The rise in time of the arsenazo signal evoked by a light flash shows two phases. In strontium saline we observe a fast increase at the onset of the arsenazo signal which is detectable within the first 20-100 ms of the signal rise and a slow further increase to the maximum, with a duration of 0.7-6 s. In the detailed analysis of both phases we observed that the amplitude of each phase increases supralinear, i.e. disproportionate to the stimulus intensity. The fast rising phase of the arsenazo signal is not visibly voltage-depen-dent. This fast rising phase might be a monitor of an IP3-sensitive calcium or strontium release. Since the amplitude of the fast rising phase increases supralinear with the stimulus intensity, we propose the interpretation that more than one IP3-molecule must bind to the IP3-receptor to open this channel of the intracellular calcium store. Only the slow rising phase is voltage-dependent. The kinetic of this slow rising phase was accelerated with more negative membrane potentials. This predominant slow phase correlates with the receptor current-time integral. Therefore the slow rising phase of the arsenazo signal might be a monitor for influx of calcium or strontium through light activated ion channels in the plasma membrane. The supralinearity of the amplitude of the slow rising phase might indicate the supralinear increase in calcium or strontium, which is carried by the receptor current. A ddi­ tionally, we calculated the fraction of strontium and calcium ions of the total receptor current. When calcium was replaced by strontium in the superfusate about 3-30% of the receptor current are carried by strontium and calcium ions. In physiological saline calcium contributes about 1-1.5% to the receptor current. 
  Reference    Z. Naturforsch. 52c, 536—548 (1997); received March 17/April 11 1997 
  Published    1997 
  Keywords    Limulus Ventral Photoreceptors, Intracellular Arsenazo Signal, Cytosolic Calcium or Strontium Transient, Cooperative Calcium Release 
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 TEI-XML for    default:Reihe_C/52/ZNC-1997-52c-0536.pdf 
 Identifier    ZNC-1997-52c-0536 
 Volume    52