Differential effects of propranolol on the IgE-dependent, or calcium ionophore-stimulated, phosphoinositide hydrolysis and calcium mobilization in a mast (RBL 2H3) cell line.
Our previous studies demonstrated that propranolol, an inhibitor of phosphatidic acid phosphohydrolase (PAPase) (EC 3.1.3.4) blocks the IgE-dependent mediator release from a rat mast (RBL 2H3) cell line. To continue these studies, we examined the ability of propranolol to inhibit the IgE-dependent or ionomycin-mediated phosphoinositide hydrolysis and calcium mobilization in RBL 2H3 cells. RBL 2H3 cells, sensitized with mouse monoclonal anti-trinitrophenol IgE (anti-TNP IgE), were stimulated to release both histamine and peptidoleukotrienes (LT) in response to a suboptimal concentration of trinitrophenol-ovalbumin conjugate (TNP-OVA) or ionomycin. Preincubation of the cells with d,l-propranolol (300 microM) significantly (P less than 0.05) inhibited the effects of both TNP-OVA and ionomycin on histamine and LT release. There was no difference in potency for the different isomers of propranolol, indicating that these effects were not a consequence of an effect on beta 2-adrenergic receptors. TNP-OVA produced a rapid hydrolysis of phosphoinositides resulting in a time-dependent increase in mono- (IP1), di- (IP2), tri- (IP3), and total inositol phosphate production. Ionomycin also produced a rapid increase in total inositol phosphate production; however, this largely reflected an accumulation of IP1. Both secretagogues produced a rapid elevation in cytosolic free calcium ([Ca2+]i); however, the effect of ionomycin maximized within a much shorter time frame than the effect of TNP-OVA. The effects of TNP-OVA on phosphoinositide hydrolysis and increase in [Ca2+]i were inhibited by propranolol over exactly the same concentration range as the effects of this compound on TNP-OVA-stimulated mediator release. In contrast, propranolol had no effect on the increase in [Ca2+]i and phosphoinositide hydrolysis in response to ionomycin. Taken together, these results suggest that PAPase/phospholipase D (PLD) (EC 3.1.4.4) activation may be a prerequisite for both IgE-dependent and ionomycin-stimulated mediator release from RBL 2H3 cells. Although other explanations are possible, the data further suggest that receptor-mediated, but not ionophore-stimulated, phosphoinositide hydrolysis and [Ca2+]i in RBL 2H3 cells may be regulated by a propranolol-sensitive pathway involving possible activation of PAPase.
Lin
P Y
PY
Department of Pharmacology, Hoffmann-La Roche, Nutley, NJ 07110.
Wiggan
G A
GA
Welton
A F
AF
Gilfillan
A M
AM
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D004075:Diglycerides / Q000096:biosynthesis; D006636:Histamine Release / Q000187:drug effects; D006868:Hydrolysis; D007073:Immunoglobulin E / Q000378:metabolism / Q000502:physiology*; D015759:Ionomycin / Q000494:pharmacology*; D015289:Leukotrienes / Q000378:metabolism; D008407:Mast Cells / Q000187:drug effects / Q000378:metabolism*; D010047:Ovalbumin / Q000494:pharmacology*; D010711:Phosphatidate Phosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism; D010712:Phosphatidic Acids / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D010739:Phospholipase D / Q000378:metabolism / Q000502:physiology; D011433:Propranolol / Q000494:pharmacology*; D015398:Signal Transduction; D013268:Stimulation, Chemical
D004075:Diglycerides; D015289:Leukotrienes; D010712:Phosphatidic Acids; D010716:Phosphatidylinositols; C038600:trinitrophenyl-ovalbumin; D007073:Immunoglobulin E; D015759:Ionomycin; D010047:Ovalbumin; D011433:Propranolol; D010711:Phosphatidate Phosphatase; D010739:Phospholipase D; D002118:Calcium