Hypotonically induced calcium release from intracellular calcium stores.
Osmotic cell swelling induced by hypotonic stress is associated with a rise in intracellular Ca2+ concentration, which is at least partly due to a release of Ca2+ from internal stores. Since osmotic influx of water dilutes the cytoplasmic milieu, we have investigated how nonmitochondrial Ca2+ stores in permeabilized A7r5 cells respond to a reduction in cytoplasmic tonicity. We now present experimental evidence for a direct Ca2+ release from the stores when exposed to a hypotonic medium. The release is graded, but does not occur through the inositol trisphosphate or the ryanodine receptor. Ca2+ seems to be released through the passive leak pathway, and this phenomenon can be partially inhibited by divalent cations in the following order of potency: Ni2+ = Co2+ > Mn2+ > Mg2+ > Ba2+. This release also occurs in intact A7r5 cells. This novel mechanism of hypotonically induced Ca2+ release is therefore an inherent property of the stores, which can occur in the absence of second messengers. Intracellular stores can therefore act as osmosensors.
Missiaen
L
L
Laboratorium voor Fysiologie, K. U. Leuven Campus Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium.
De Smedt
H
H
Parys
J B
JB
Sienaert
I
I
Vanlingen
S
S
Droogmans
G
G
Nilius
B
B
Casteels
R
R
D000818:Animals; D001011:Aorta; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent / Q000494:pharmacology*; D002460:Cell Line; D002463:Cell Membrane Permeability; D003593:Cytoplasm / Q000378:metabolism; D007038:Hypotonic Solutions; D007700:Kinetics; D009131:Muscle, Smooth, Vascular; D051381:Rats; D013997:Time Factors
D002413:Cations, Divalent; D007038:Hypotonic Solutions; D002118:Calcium