INHIBITION OF BRADYKININ-INDUCED CYTOSOLIC CA2+ ELEVATION BY MUSCARINIC STIMULATION WITHOUT ATTENUATION OF INOSITOL 1,4,5-TRISPHOSPHATE PRODUCTION IN HUMAN NEUROBLASTOMA SK-N-BE(2)C CELLS

Abstract

Cross talk between two phospholipase C (PLC)-linked receptor signalings was investigated in SK-N-BE(2)C human neuroblastoma cells. Sequential stimulation with two agonists at 5-min intervals was performed to examine the interaction between muscarinic and bradykinin (BK) receptors. Pretreatment of cells with a maximal effective concentration (5 mu M) of BK did not affect the subsequent carbachol (CCh)-induced [Ca2+](i) rise, but CCh (1 mM) pretreatment completely abolished the BK-induced [Ca2+](i) rise without inhibition of BK-induced inositol 1,4,5-trisphosphate (IP3) generation. Thapsigargin (1 mu M) pretreatment abolished the subsequent BK- and CCh-induced [Ca2+](i) rise, though it did not affect agonist-induced IP3 generation. However, the addition of atropine at plateau phases of CCh-induced [Ca2+](i) rise and IP3 production caused a rapid decline to the basal levels and then restored the [Ca2+](i) rise by BK. Treatment of cells with both CCh and BK at the same time showed additive effects in IP3 production. However, the [Ca2+](i) rise induced by both agonists in the presence or absence of extracellular Ca2+ was the same as the responses triggered by CCh alone. The results suggest that each receptor or receptor-linked PLC activity is not influenced by pretreatment with the other agonist but IP3-sensitive Ca2+ stores are shared by signal pathways from both receptors.