Phosphatidylinositol hydrolysis and calcium signaling

The salivary glands of the blowfly possess two separate 5-HT receptors. One receptor system is linked to adenylate cyclase to produce cyclic AMP, which regulates cation transport across the epithelium. The other receptor acts through calcium, which stimulates anion transport. Activation of this second receptor is associated with the specific hydrolysis of phosphatidylinositol (PI) to give a PI response that appears to be a characteristic feature of receptors that act through calcium. Studies on this insect gland have established a close correlation between PI hydrolysis and changes in calcium gating. The idea that these two receptor-mediated events might be intimately related was strengthened by the observation that the ability of 5-HT to gate calcium could be varied by adjusting the level of PI in the membrane.