Acetylcholine stimulated phosphatidylinositol turnover

Our studies also suggest that a detailed differentiation has to be made between turnover and dc. yiOVO biosynthesis of complex lipids, mainly in the case of IPG and PA. Phosphatidylinositol is a minor component of membranes that has been implicated since long ago in the cell responses to hormones, neurotransmitters, and other agents (Hokin, 1977). In recent years from studies on synaptosomes the proposal has been made that PA phosphatase is stimulated by acetylcholine (Yagihara et al., 1973 Schacht Agranoff 1973, 1974). 

Although there is an increased turnover of phosphatidylinositol in stimulated tissue, the primary action of acetylcholine is to cause a net breakdown of this phosphatide. The breakdown was first observed as a loss of radioactivity from prelabeled phosphatidylinositol in response to acetylcholine in the avian salt gland (Hokin, M.R. ... 

To summarize these changes which I have discussed, stimulation of salt gland and pancreas with acetylcholine leads to a breakdown of phosphatidylinositol. Under some conditions, the (18 0,20 4)-diglyceride moiety of this phosphatidylinositol is converted almost quantitatively to (18 0,20 4)phosphatidic acid. During the stimulated state, this novel species of phosphatidic acid undergoes continuous turnover of its phosphate group, presumably with (18 0, 20 4)diglyceride as an intermediate. It is specifically used for the resynthesis of phosphatidylinositol when stimulated tissue reverts to the unstimulated state (Fig. 1). 

The hormone pancreozymin (cholecystokinin-pancreoz3miin) stimulates the protein secretory cycle in the exocrine pancreas (Harper Raper, 1943) it also elicits phosphatidylinositol breakdown, formation of phosphatidic acid, and increased turnover of the polar headgroups of these phosphatides. These effects are essentially the same as those observed in response to acetylcholine (Hokin, M.R.,... 

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