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pubmed:abstractText |
Muscarinic cholinergic stimulation of rat cerebral nerve endings incubated with 32Pi causes an enhancement of the labeling of phosphatidic acid (PA) and phosphatidylinositol (PI). The involvement of Ca2+ in the stimulation of PA and PI labeling by carbamylcholine (CCh) was investigated. Enhancement of Ca2+-influx with veratridine and the Ca2+-ionophore A23187 caused a vast decrease of the labeling of the polyphosphoinositides, which was not accompanied by an enhancement of the labeling of PA and PI. The dihydropyridine Ca2+-agonist BAY K8644 did not affect phospholipid labeling. A23187, veratridine and BAY K 8644 did not enhance stimulation of the labeling of PA and PI by CCh. When Ca2+ was omitted from the incubation, A23187 caused an enhancement of basal and CCh-stimulated labeling of PA and PI, possibly indicating a particular feature of A23187 unrelated to its iontophoretic properties. The Ca2+-channel antagonists nimodipine, verapamil and flunarizine were virtually without effect on basal and CCh-stimulated labeling of PI and PA. These data support the notion that the muscarinic cholinergic inositide response is not mediated or controlled by Ca2+-flux.
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