title: Alpha1-adrenergic receptor signaling is localized to caveolae in neonatal rat cardiomyocytes.
abstract: In neonatal rat cardiomyocytes, phosphatidylinositol(4,5)bisphosphate (PIP2) is a precursor of second messengers, a stabilizer of ion channels and exchangers, an anchor point for the cytoskeleton and, in addition, can serve as a signaling molecule in its own right. We examined the possibility that sarcolemmal PIP2 exists in different pools and that only one of these provides the substrate for alpha1-adrenergic receptor activated phospholipase C (PLC). Membranes were separated on the basis of buoyant density, and the light lipid raft fractions were further separated into caveolae and non-caveolar rafts using immunoprecipitation. PIP2 was principally located in the light lipid raft fractions and was equally distributed between caveolae and non-caveolar membranes. Heavier membrane fractions also contained some PIP2. Addition of the alpha1-adrenergic receptor agonist phenylephrine (50 microM) caused reductions in PIP2, but only in caveolae. PIP2 in other fractions was unaffected. In agreement with this, PLCbeta1 and, to a lesser extent, Galphaq were concentrated in this fraction. PLCbeta3 was primarily observed in heavier membranes. We conclude that PIP2 in cardiomyocyte sarcolemma is compartmentalized and that alpha1-adrenergic receptor signaling is localized to caveolae.
authors.affiliation: Cellular Biochemistry Laboratory, Baker Heart Research Institute, PO Box 6492 St. Kilda Road Central, Melbourne, 8008 Victoria, Australia.
authors.forename: James B
authors.initials: JB
authors.lastname: Morris
authors.forename: Huy
authors.initials: H
authors.lastname: Huynh
authors.forename: Oliver
authors.initials: O
authors.lastname: Vasilevski
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Woodcock
mesh_terms: D058646:Adrenergic alpha-1 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D021941:Caveolae / Q000378:metabolism*; D051244:Caveolin 3 / Q000378:metabolism; D002478:Cells, Cultured; D007527:Isoenzymes / Q000378:metabolism; D021962:Membrane Microdomains / Q000737:chemistry / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D054799:Phospholipase C beta; D010743:Phospholipids / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism*; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D058646:Adrenergic alpha-1 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D051244:Caveolin 3; D007527:Isoenzymes; D019269:Phosphatidylinositol 4,5-Diphosphate; D010743:Phospholipids; D018340:Receptors, Adrenergic, alpha-1; D010656:Phenylephrine; D010738:Type C Phospholipases; D054799:Phospholipase C beta