Spatiotemporal patterning of IP3-mediated Ca2+ signals in Xenopus oocytes by Ca2+-binding proteins.
Ca(2+)-binding proteins (CaBPs) are expressed in a highly specific manner across many different cell types, yet the physiological basis underlying their selective distribution patterns remains unclear. We used confocal line-scan microscopy together with photo-release of IP(3) in Xenopus oocytes to investigate the actions of mobile cytosolic CaBPs on the spatiotemporal properties of IP(3)-evoked Ca(2+) signals. Parvalbumin (PV), a CaBP with slow Ca(2+)-binding kinetics, shortened the duration of IP(3)-evoked Ca(2+) signals and 'balkanized' global responses into discrete localized events (puffs). In contrast, calretinin (CR), a presumed fast buffer, prolonged Ca(2+) responses and promoted 'globalization' of spatially uniform Ca(2+) signals at high [IP(3)]. Oocytes loaded with CR or PV showed Ca(2+) puffs following photolysis flashes that were subthreshold in controls, and the spatiotemporal properties of these localized events were differentially modulated by PV and CR. In comparison to results we previously obtained with exogenous Ca(2+) buffers, PV closely mimicked the actions of the slow buffer EGTA, whereas CR showed important differences from the fast buffer BAPTA. Most notably, puffs were never observed after loading BAPTA, and this exogenous buffer did not show the marked sensitization of IP(3) action evident with CR. The ability of Ca(2+) buffers and CaBPs with differing kinetics to fine-tune both global and local intracellular Ca(2+) signals is likely to have significant physiological implications.
Dargan
Sheila L
SL
Department of Neurobiology and Behaviour, University of California Irvine, CA 92697-4550, USA.
Schwaller
Beat
B
Parker
Ian
I
D000818:Animals; D064032:Calbindin 2; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects* / Q000502:physiology; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates / Q000378:metabolism*; D008845:Microinjections; D009865:Oocytes / Q000502:physiology; D010320:Parvalbumins / Q000494:pharmacology*; D010777:Photochemistry; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D064030:S100 Calcium Binding Protein G / Q000494:pharmacology*; D014982:Xenopus laevis
D064032:Calbindin 2; D015220:Calcium Channels; D002614:Chelating Agents; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates; D010320:Parvalbumins; D018160:Receptors, Cytoplasmic and Nuclear; D064030:S100 Calcium Binding Protein G; C092449:inositol 1,2,3-trisphosphate; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid