Temperature dependence of agonist-stimulated Ca2+ signaling in cultured endothelial cells.
In cultured endothelial cells, the temperature dependence of bradykinin-initiated Ca2+ signaling was studied using Fura-2 technique. Initially, the temperature dependence of the dissociation constant of Fura-2 for Ca2+ was investigated. Temperature-initiated changes in the apparent dissociation constant (K'D) using the ratio (F340/F380) were due to a hypsochromic shift in excitation wavelengths and changes in the effective dissociation constant of Fura-2 for Ca2+ (K"D). Equations were provided to correct the dissociation constant for Fura-2, either for using the common ratio (F340/F380) or the shift corrected ratio (F340-delta lambda/F380-delta lambda). In a simple experimental protocol, the temperature dependence of the transient increase in free intracellular Ca2+ to bradykinin (i.e. Ca2+ release, sequestration and extrusion) and Ca2+/Mn2+ entry through a Ca2+ store-operated Ca2+ entry pathway (SOCP) were determined. While the temperature dependence of intracellular Ca2+ release, sequestration and extrusion (i.e. enzymatically controlled phenomena) were found to follow the same exponential function [t = A x e(-B x T); t, reaction time; A, B, constants; T, experimental temperature in K; K = degree C + 273], Ca2+/Mn2+ entry upon ion application to pre-stimulated cells strictly followed Fick's law of diffusion [t = A x (1/T) x e(B/T); t, reaction time; A, B, constants; T, experimental temperature in K]. In contrast to the temperature dependence of bradykinin-stimulated Ca2+/Mn2+ entry, the temperature dependence of Mn2+ entry on addition of agonist did not correlate with Fick's law of diffusion, but followed the same exponential function obtained for Ca2+ release, sequestration and extrusion. In conclusion, these data suggest that activation of SOCP by autacoid is due to enzymatic mechanism(s), while Ca2+ entry through SOCP, once activated, is due to a diffusion-like phenomenon.
Paltauf-Doburzynska
J
J
Department of Medical Biochemistry, University of Graz, Austria.
Graier
W F
WF
D000818:Animals; D001011:Aorta / Q000166:cytology; D001920:Bradykinin / Q000494:pharmacology*; D002118:Calcium / Q000819:agonists / Q000378:metabolism*; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000737:chemistry; D015398:Signal Transduction; D013050:Spectrometry, Fluorescence; D013552:Swine; D013696:Temperature
D005456:Fluorescent Dyes; D001920:Bradykinin; D002118:Calcium; D016257:Fura-2