Calcium regulation of hormonal-sensitive phospholipase C.

Numerous hormones or neurotransmitters regulate the activity of their target cell via the activation of a specific phospholipase C. Two intracellular second messengers are generated, diacylglycerol which activates protein kinase C and inositol (1,4,5)P3 which mobilizes calcium from intracellular stores. Both these molecules trigger within the cell biological effects associated with the hormone considered. In these transduction mechanisms, calcium mobilization is a consequence of primary activation of phospholipase C. However calcium is also able to regulate phospholipase C activity since, in many cellular systems, calcium by itself stimulates phosphoinositol lipid metabolism. Such results imply that all molecules which modify the intracellular calcium concentration may be considered as potent regulators of phospholipase C activity. Data obtained on different cell systems favours this hypothesis: Activators of calcium influx stimulate intracellular inositol phosphate accumulation and molecules which reduce intracellular calcium concentration reduce inositol phosphate production. Thus calcium may play an important role in the regulation of hormonal sensitive phospholipase C activities.