Cytosolic Ca(2+) controls the loading dependence of IP(3)-induced Ca(2+) release.
It is still debated whether inositol 1,4, 5-trisphosphate(IP(3))-induced Ca(2+) release is loading-dependent. We now report that stimulation of the IP(3) receptor by luminal Ca(2+) depends on the cytosolic [Ca(2+)] in permeabilized A7r5 cells. The EC(50) and maximal extent of Ca(2+) release were loading-dependent in the presence of 5 mM 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid: the EC(50) increased 1.9-fold and the maximal release decreased from 88 to 52% when the stores contained 73% less Ca(2+). In the presence of 0.3 microM free Ca(2+), the EC(50) for filled and less filled stores differed, however, only 1.2-fold and the maximal Ca(2+) release was respectively 96 and 87% of the total releasable Ca(2+). At 1 microM free Ca(2+), the difference in EC(50) between filled and less filled stores again became larger (2.2-fold) and the maximal Ca(2+) release decreased from 93 to 87% when the stores contained less Ca(2+).
Missiaen
L
L
Laboratorium voor Fysiologie, K. U. Leuven Campus Gasthuisberg O/N, Herestraat 49, Leuven, B-3000, Belgium. Ludwig.Missiaen@med.kuleuven.ac.be
De Smedt
H
H
Parys
J B
JB
Van Acker
K
K
De Smet
P
P
Callewaert
G
G
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D017136:Ion Transport; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D051381:Rats
D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium