We have studied receptor-mediated phosphoinositide (PI) hydrolysis by phospholipase C in neuroblastoma x brain cell hybrid NCB-20 cells. Stimulation of muscarinic cholinergic, histaminergic and bradykinin receptors was found to increase PI turnover measured by accumulation of 3H-inositol monophosphate in the presence of lithium. The PI response of muscarinic and histaminergic receptors were highly sensitive to the M1 receptor antagonist pirenzepine and histamine H1 receptor antagonist triprolidine, respectively, while the bradykinin response was potently blocked by a bradykinin antagonist B 4881. All three types of PI response appeared to be additive and required unusually high concentration of lithium to display the maximal accumulation of inositol phosphates. The effects mediated by muscarinic and bradykinin receptors were largely dependent upon extracellular calcium but only partially attenuated by pertussis toxin. Preexposure of cells to muscarinic receptor agonist carbachol or bradykinin resulted in homologous desensitization to subsequent receptor stimulation. Phorbol esters also elicited desensitization of these receptor mediated PI response, suggesting a possible role of protein kinase C in this desensitization process. Phospholipase activity can also be enhanced by activators of voltage-sensitive sodium channels such as batrachotoxin and veratridine and sodium ionophore such as monensin. Moreover, veratridine can modulate the PI response mediated by muscarinic receptors. NCB-20 cell is an ideal system to study the mechanism, regulation and neurophysiological role of receptor-mediated Pl turnover.
