Activation of Ca2+ entry into acinar cells by a non-phosphorylatable inositol trisphosphate.
In many cell types, receptor activation of phosphoinositidase C results in an initial release of intracellular Ca2+ stores followed by sustained Ca2+ entry across the plasma membrane. Inositol 1,4,5-trisphosphate is the mediator of the initial Ca2+ release, although its role in the mechanism underlying Ca2+ entry remains controversial. We have now used two techniques to introduce inositol phosphates into mouse lacrimal acinar cells and measure their effects on Ca2+ entry: microinjection into cells loaded with Fura-2, a fluorescent dye which allows the measurement of intracellular free calcium concentration by microspectrofluorimetry, and perfusion of patch clamp pipettes in the whole-cell configuration while monitoring the activity of Ca(2+)-activated K+ channels as an indicator of intracellular Ca2+. We report here that inositol 1,4,5-trisphosphate serves as a signal that is both necessary and sufficient for receptor activation of Ca2+ entry across the plasma membrane in these cells.
Bird
G S
GS
Calcium Regulation Section, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709.
Rossier
M F
MF
Hughes
A R
AR
Shears
S B
SB
Armstrong
D L
DL
Putney
J W
JW
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism / Q000494:pharmacology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates / Q000378:metabolism / Q000494:pharmacology*; D007765:Lacrimal Apparatus / Q000187:drug effects / Q000378:metabolism; D016210:Methacholine Chloride / Q000494:pharmacology; D051379:Mice; D010766:Phosphorylation; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D011956:Receptors, Cell Surface / Q000502:physiology; D018160:Receptors, Cytoplasmic and Nuclear; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates; D015221:Potassium Channels; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D013729:Terpenes; D016210:Methacholine Chloride; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; C062616:inositol 2,4,5-trisphosphate; D002118:Calcium