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Controlof IP 3 ‐mediated Ca 2+ puffs in Xenopus laevis oocytes by the Ca 2+ ‐binding protein parvalbumin
Author(s) -
John Linu M.,
MosqueraCaro Monica,
Camacho Patricia,
Lechleiter James D.
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.t01-2-00003.x
Subject(s) - bapta , parvalbumin , xenopus , egta , divalent , biophysics , chemistry , calcium , calbindin , microbiology and biotechnology , receptor , biochemistry , biology , neuroscience , organic chemistry , gene
1 Elementary events of Ca 2+ release (Ca 2+ puffs) can be elicited from discrete clusters of inositol 1,4,5 trisphosphate receptors (IP 3 Rs) at low concentrations of IP 3 . Ca 2+ puffs have rarely been observed unless elicited by either hormone treatment or introduction of IP 3 into the cell. However, cells appear to have sufficient concentrations of IP 3 (0.1‐3.0 μM) to induce Ca 2+ release under resting conditions. 2 Here, we investigated Ca 2+ puff activity in non‐stimulated Xenopus oocytes using confocal microscopy. The fluorescent Ca 2+ dye indicators Calcium Green 1 and Oregon Green 488 BAPTA‐2 were injected into oocytes to monitor basal Ca 2+ activity. 3 In this preparation, injection or overexpression of parvalbumin, an EF‐hand Ca 2+ ‐binding protein (CaBP), induced Ca 2+ puffs in resting Xenopus oocytes. This activity was inhibited by heparin, an IP 3 R channel blocker, and by mutation of the Ca 2+ ‐binding sites in parvalbumin. 4 Ca 2+ puff activity was also evoked by injection of low concentrations of the Ca 2+ chelator EGTA, but not by calbindin D 28k , another member of the EF‐hand CaBP superfamily. 5 BAPTA and the Ca 2+ indicator dye Oregon Green 488 BAPTA‐1 evoked Ca 2+ puff activity, while the dextran conjugate of Oregon Green 488 BAPTA‐1 did not. These data indicate that a Ca 2+ buffer must be mobile in order to increase Ca 2+ puff activity. 6 Together, the data indicate that some IP 3 Rs spontaneously release Ca 2+ under resting concentrations of IP 3 . These elementary Ca 2+ events appear to be below the level of detection of current imaging techniques. We suggest that parvalbumin evokes Ca 2+ puffs by coordinating the activity of elementary IP 3 R channel openings. 7 We conclude that Ca 2+ release can be evoked not only by hormone‐induced increases in IP 3 , but also by expression of mobile cytosolic CaBPs under resting concentrations of IP 3 .