In PC12 cells, cultured in the presence of nerve growth factor to increase their complement of muscarinic receptors, treatment with carbachol induces muscarinic receptor-dependent rises in free cytosolic Ca2+ as well as hydrolysis of membrane phosphoinositides. Experiments were carried out to clarify the relationship between these two receptor-triggered events. In particular, since inositol-1,4,5-trisphosphate (the hydrophilic metabolite produced by the hydrolysis of phosphatidylinositol-4,5-bisphosphate) is believed to mediate intracellularly the release of Ca2+ from nonmitochondrial store(s), it was important to establish whether it can be generated at resting cytoplasmic concentration of Ca2+ (approximately 0.1 microM). Cells incubated in Ca2+-free medium were depleted of their cytoplasmic Ca2+ stores by pretreatment with ionomycin. When these cells were then treated with carbachol, their cytosolic concentration of Ca2+ remained at the resting level, whereas inositol-1,4,5-trisphosphate generation was still markedly stimulated. Our results demonstrate that an increase in the concentration of cytosolic Ca2+ is not a necessary intermediate between receptor activation and phosphoinositide hydrolysis, and therefore support the second-messenger role of inositol-1,4,5-trisphosphate.
Muscarinic receptor-induced phosphoinositide hydrolysis at resting cytosolic Ca2+ concentration in PC12 cells.
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L M Vicentini, A Ambrosini, F Di Virgilio, T Pozzan, J Meldolesi; Muscarinic receptor-induced phosphoinositide hydrolysis at resting cytosolic Ca2+ concentration in PC12 cells.. J Cell Biol 1 April 1985; 100 (4): 1330–1333. doi: https://doi.org/10.1083/jcb.100.4.1330
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