Muscarinic Receptors Stimulate Ca2+ Influx via Phospholipase A2 Pathway in Ileal Smooth Muscles

Abstract

Receptor-mediated changes in intracellular Ca2+ in ileal longitudinal smooth muscles of guinea pig were studied. Stimulation of muscarinic receptors by carbachol induced both Ca2+-influx through plasma membranes and Ca2+release from intracellular stores. Pretreatment of the muscle with an inhibitor of phospholipase A2 abolished the Ca2+-influx but not the Ca2+-release, whereas an inhibitor of phospholipase C showed opposite effects. The inhibitors of cyclooxygenase and lipoxygenase enhanced the muscarinic receptor-induced Ca2+-influx. Addition of arachidonic acid mimic the receptor-induced Ca2+-influx. Treatment of muscles with pertussis toxin abolished the receptor-induced release of arachidonic acid as well as Ca2+-influx but was less effective on the IP3 formation and the Ca2+-release. Taken together, our results suggest that phospholipase A2 but not phospholipase C pathway is involved in the muscarinic receptor-induced Ca2+-influx in ileal smooth muscle.