TY - JOUR
T1 - Control of IP3-mediated Ca2+ puffs in Xenopus laevis oocytes by the Ca2+-binding protein parvalbumin
AU - John, Linu M.
AU - Mosquera-Caro, Monica
AU - Camacho, Patricia
AU - Lechleiter, James D.
PY - 2001/8/15
Y1 - 2001/8/15
N2 - 1. Elementary events of Ca2+ release (Ca2+ puffs) can be elicited from discrete clusters of inositol 1,4,5 trisphosphate receptors (IP3Rs) at low concentrations of IP3. Ca2+ puffs have rarely been observed unless elicited by either hormone treatment or introduction of IP3 into the cell. However, cells appear to have sufficient concentrations of IP3 (0.1-3.0 μM) to induce Ca2+ release under resting conditions. 2. Here, we investigated Ca2+ puff activity in non-stimulated Xenopus oocytes using confocal microscopy. The fluorescent Ca2+ dye indicators Calcium Green 1 and Oregon Green 488 BAPTA-2 were injected into oocytes to monitor basal Ca2+ activity. 3. In this preparation, injection or overexpression of parvalbumin, an EF-hand Ca2+-binding protein (CaBP), induced Ca2+ puffs in resting Xenopus oocytes. This activity was inhibited by heparin, an IP3R channel blocker, and by mutation of the Ca2+-binding sites in parvalbumin. 4. Ca2+ puff activity was also evoked by injection of low concentrations of the Ca2+ chelator EGTA, but not by calbindin D28k, another member of the EF-hand CaBP superfamily. 5. BAPTA and the Ca2+ indicator dye Oregon Green 488 BAPTA-1 evoked Ca2+ puff activity, while the dextran conjugate of Oregon Green 488 BAPTA-1 did not. These data indicate that a Ca2+ buffer must be mobile in order to increase Ca2+ puff activity. 6. Together, the data indicate that some IP3Rs spontaneously release Ca2+ under resting concentrations of IP3. These elementary Ca2+ events appear to be below the level of detection of current imaging techniques. We suggest that parvalbumin evokes Ca2+ puffs by coordinating the activity of elementary IP3R channel openings. 7. We conclude that Ca2+ release can be evoked not only by hormone-induced increases in IP3, but also by expression of mobile cytosolic CaBPs under resting concentrations of IP3.
AB - 1. Elementary events of Ca2+ release (Ca2+ puffs) can be elicited from discrete clusters of inositol 1,4,5 trisphosphate receptors (IP3Rs) at low concentrations of IP3. Ca2+ puffs have rarely been observed unless elicited by either hormone treatment or introduction of IP3 into the cell. However, cells appear to have sufficient concentrations of IP3 (0.1-3.0 μM) to induce Ca2+ release under resting conditions. 2. Here, we investigated Ca2+ puff activity in non-stimulated Xenopus oocytes using confocal microscopy. The fluorescent Ca2+ dye indicators Calcium Green 1 and Oregon Green 488 BAPTA-2 were injected into oocytes to monitor basal Ca2+ activity. 3. In this preparation, injection or overexpression of parvalbumin, an EF-hand Ca2+-binding protein (CaBP), induced Ca2+ puffs in resting Xenopus oocytes. This activity was inhibited by heparin, an IP3R channel blocker, and by mutation of the Ca2+-binding sites in parvalbumin. 4. Ca2+ puff activity was also evoked by injection of low concentrations of the Ca2+ chelator EGTA, but not by calbindin D28k, another member of the EF-hand CaBP superfamily. 5. BAPTA and the Ca2+ indicator dye Oregon Green 488 BAPTA-1 evoked Ca2+ puff activity, while the dextran conjugate of Oregon Green 488 BAPTA-1 did not. These data indicate that a Ca2+ buffer must be mobile in order to increase Ca2+ puff activity. 6. Together, the data indicate that some IP3Rs spontaneously release Ca2+ under resting concentrations of IP3. These elementary Ca2+ events appear to be below the level of detection of current imaging techniques. We suggest that parvalbumin evokes Ca2+ puffs by coordinating the activity of elementary IP3R channel openings. 7. We conclude that Ca2+ release can be evoked not only by hormone-induced increases in IP3, but also by expression of mobile cytosolic CaBPs under resting concentrations of IP3.
UR - http://www.scopus.com/inward/record.url?scp=0035880849&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0035880849&partnerID=8YFLogxK
U2 - 10.1111/j.1469-7793.2001.t01-2-00003.x
DO - 10.1111/j.1469-7793.2001.t01-2-00003.x
M3 - Article
C2 - 11507154
AN - SCOPUS:0035880849
SN - 0022-3751
VL - 535
SP - 3
EP - 16
JO - Journal of Physiology
JF - Journal of Physiology
IS - 1
ER -