Luminal Ca2+ controls the activation of the inositol 1,4,5-trisphosphate receptor by cytosolic Ca2+.
Luminal Ca2+ controls the sensitivity of the intracellular Ca2+ stores to inositol 1,4,5-trisphosphate (Ins(1,4,5)P3). Ins(1,4,5)P3-induced Ca2+ release is also controlled by cytosolic Ca2+; low concentrations of Ca2+ stimulate the release. The aim of this work was to investigate whether luminal Ca2+ would affect the stimulation of the Ins(1,4,5)P3 receptor by cytosolic Ca2+ in permeabilized A7r5 smooth muscle cells. We also report that the Ins(1,4,5)P3 receptor in A7r5 cells is activated by low concentrations of cytosolic Ca2+. Cytoplasmic Ca2+ increases the Ins(1,4,5)P3 sensitivity without affecting the cooperativity. The increase in Ins(1,4,5)P3 sensitivity becomes relatively more pronounced when the Ca2+ content of the stores decreases. This modulatory effect of luminal Ca2+ on the responsiveness to cytosolic Ca2+ is an intrinsic property of the Ins(1,4,5)P3 receptor.
Missiaen
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Laboratorium voor Fysiologie, K. U. Leuven, Belgium.
De Smedt
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Droogmans
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Casteels
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D000818:Animals; D001011:Aorta; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D015220:Calcium Channels; D002460:Cell Line; D002463:Cell Membrane Permeability; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism* / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007700:Kinetics; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D004533:Egtazic Acid; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium