Kinetics of the non-specific calcium leak from non-mitochondrial calcium stores in permeabilized A7r5 cells.
We have investigated the detailed kinetics of the passive Ca2+ leak from non-mitochondrial Ca2+ stores in permeabilized A7r5 cells. The decrease in the content of stored Ca2+ in the presence of 2 microM thapsigargin deviated from a single-exponential curve in the initial phase of the efflux. The deviation persisted after correcting this efflux for passively bound Ca2+. The non-single-exponential nature of the spontaneous release also occurred when the initial store Ca2+ content was reduced to 40% of its original value by pretreatment with 200 nM inositol 1,4,5-trisphosphate (InsP3). The passive Ca2+ leak could be modelled by two exponential curves with discrete rate constants of 0.06 min-1 and 0.98 min-1, and not by any other type of non-exponential decay. We concluded that individual store units are heterogeneous with respect to their passive Ca2+ permeability. This non-exponential nature of the passive Ca2+ release is unrelated to the non-single-exponential InsP3-induced Ca2+ release.
Missiaen
L
L
Laboratorium voor Fysiologie, K.U. Leuven Campus Gasthuisberg, Belgium.
De Smedt
H
H
Parys
J B
JB
Raeymaekers
L
L
Droogmans
G
G
Van Den Bosch
L
L
Casteels
R
R
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002463:Cell Membrane Permeability; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D017136:Ion Transport; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism; D051381:Rats
D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium