Alpha 1-adrenergic signaling in human airway epithelial cells involves inositol lipid and phosphate metabolism.
A role for phospholipase C (PLC) hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) as a mechanism of alpha 1-adrenergic signal transduction in human airway epithelial cells (AEC) was investigated in isolated normal tracheal and cystic fibrosis (CF) nasal epithelial cells grown in in vitro culture and prelabeled with 3 muCi myo-[3H]inositol/ml for 72 h. Breakdown of polyphosphoinositides was measured using thin-layer chromatography to detect phosphatidylinositol, phosphatidylinositol 4-phosphate (PIP), and PIP2. Inositol phosphates were separated by ion-exchange column chromatography. In normal AEC, the addition of the endogenous catecholamine l-epinephrine produced a rapid, transient accumulation of inositol 1,4,5-trisphosphate (IP3) and inositol 1,4-bisphosphate (IP2) and breakdown of PIP and PIP2. IP3 increased 1.7-fold and IP2 1.6-fold after 20 and 40 s, respectively. A maximal decrease of 35% PIP2 and 30% PIP is observed after 20 and 40 s, respectively. The effects of l-epinephrine were not blocked by the beta-adrenergic antagonist dl-propranolol but were mimicked by the alpha 1-adrenergic agonist methoxamine. Prazosin, an alpha 1-adrenergic antagonist, and pertussis toxin (PTX) blocked the effects of l-epinephrine and methoxamine. Addition of l-epinephrine and methoxamine to CF nasal epithelial cells also induced prazosin-sensitive polyphosphoinositide breakdown and inositol phosphate accumulation. A 2.2-fold accumulation of IP3 was observed after 10 s and 2.0-fold increase in IP2 after 20 s. Maximal decreases of 32% PIP2 and 23% PIP levels were observed after 20-s incubation with l-epinephrine. PTX reduced the effects of l-epinephrine and significantly blocked the effects of methoxamine.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Pediatrics, Rainbow Babies and Children Hospital, Cleveland, Ohio.
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Liedtke
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology; D006801:Humans; D007294:Inositol / Q000378:metabolism*; D007295:Inositol Phosphates / Q000378:metabolism; D050356:Lipid Metabolism; D008729:Methoxamine / Q000494:pharmacology; D037342:Pertussis Toxin; D010710:Phosphates / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000037:antagonists & inhibitors; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D012143:Respiratory Physiological Phenomena; D012137:Respiratory System / Q000166:cytology; D015398:Signal Transduction; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D007295:Inositol Phosphates; D010710:Phosphates; D010716:Phosphatidylinositols; D011942:Receptors, Adrenergic, alpha; D010566:Virulence Factors, Bordetella; D007294:Inositol; D037342:Pertussis Toxin; D008729:Methoxamine; D004837:Epinephrine