Chick embryo muscarinic and purinergic receptors activate cytosolic Ca 2+ via phosphatidylinositol metabolism

Abstract

In dissociated cells from chick embryos or from chick limb buds, acetylcholine (ACh) induced an increase in cellular levels of inositol 1,4,5-trisphosphate (Ins-P 3) and of inositol 1,3,4,5-tetrakisphosphate (Ins-P 4). The concentration of Ins-P 3 was enhanced transiently, whereas the level of Ins-P 4 remained elevated for at least 20 min after addition of ACh. In most cases the increase in Ins-P 4 levels was more pronounced than that of Ins-P 3 levels. The inhibition of the ACh-induced inositolphosphate response by atropine (half-maximal inhibition at 10 n M) indicates the involvement of muscarinic receptors, which in chick embryo cells induce a transient rise and a following persistent elevation of cytosolic Ca 2+ activity (G. Oettling et al. (1989) J. Dev. Physiol. 12, 85–94). Adenosine 5′-triphosphate (ATP) elicited a similar transient rise in cytosolic Ca 2+ activity, however, without a subsequent plateau. ATP also caused an increase in inositololigophosphate levels. Thus, both muscarinic and purinergic receptors in chick embryo cells are coupled to phospholipase C. The enzymatically formed Ins-P 3 mediates the release of Ca 2+ from internal stores. The Ca 2+ signal could be involved in embryonic cell migration during morphogenesis.