The effects of β-phorbol-12,13 dibutyrate on agonist-induced increases in [Ca 2+] i in N1E-115 cells : Differential modulation of responses to angiotensin II and bradykinin

Abstract

Addition of angiotensin II (A2; 500 nM) to populations of fura-2-loaded N1E-115 cells resulted in a transient increase in intracellular calcium which was abolished by pre-treatment with the phorbol ester, β-phorbol-12,13 dibutyrate (PDBu) (1.5 μM). The inhibitory effects were reversed by the protein kinase C inhibitor, staurosporin (150 nM), and down-regulation of protein kinase C was observed over 48 hr. Responses to maximally effective concentrations of histamine (300 μM), ATP (100 μM), UTP (100 μM) and carbachol (100 μM) were similarly inhibited by phorbol pre-treatment but the response to bradykinin (BK) (100 nM) was unaffected. When the concentrations of BK and A2 were adjusted to produce the same-sized calcium signals, PDBu pre-treatment abolished the response to A2 but only partially inhibited the response to BK. From the data presented here we can conclude that the calcium response to BK in N1E-115 cells is less susceptible to the inhibitory effects of protein kinase C activation than the response produced by A2.