Cholinergically stimulated phosphatidylinositol breakdown in parotid gland fragments is independent of the ionic environment

Carbamoylcholine stimulated phosphatidylinositol breakdown in rat parotid gland fragments incubated in either a Krebs Ringer medium or an ion depleted iso osmotic sucrose medium. This suggests that phosphatidylinositol breakdown is not initiated by a change in the intracellular concentration of Na⁺ or of K⁺, and previous experiments have already indicated that it is independent of cyclic nucleotides and Ca²⁺. Thus it seems that this reaction may be initiated by a direct interaction at the plasma membrane between the activated muscarinic cholinergic receptor system and the enzyme that catalyses phosphatidylinositol breakdown.