title: Protein kinase and Ca2+ modulation of myo-inositol transport in cultured retinal pigment epithelial cells.
abstract: The acute regulation of inwardly directed Na(+)-myo-inositol (MI) cotransporter activity and basal and volume-sensitive MI efflux by protein kinases C (PKC) and A (PKA), cytosolic Ca2+, and phosphoinositide (PI) turnover were characterized in cultured human retinal pigment epithelial cells using 2-[3H]MI and liquid scintillation spectrometry. Kinetic analysis revealed two distinct Na(+)-MI cotransporter components differing in apparent Michaelis constant and maximal velocity. Composite Na(+)-MI cotransport activity was stimulated by PKA activation, the muscarinic agonist carbachol, and the Ca2+ ionophore A-23187 and was inhibited by PKC activation. PKC activation also increased MI efflux, but only the volume-sensitive component, whereas PKA activation increased both basal and volume-sensitive MI efflux. These studies implicate PKC as a negative modulator of MI content through Na(+)-MI cotransport inhibition and potentiation of volume-sensitive MI efflux. PKA is a positive modulator of both Na(+)-MI cotransport and basal and volume-sensitive MI efflux. Cytosolic Ca2+ release through receptor-mediated PI hydrolysis may facilitate Na(+)-MI cotransport activity.
authors.affiliation: Department of Internal Medicine, University of Michigan, Ann Arbor 48109-0678, USA.
authors.forename: A
authors.initials: A
authors.lastname: Karihaloo
authors.forename: K
authors.initials: K
authors.lastname: Kato
authors.forename: D A
authors.initials: DA
authors.lastname: Greene
authors.forename: T P
authors.initials: TP
authors.lastname: Thomas
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D007038:Hypotonic Solutions / Q000494:pharmacology; D007294:Inositol / Q000378:metabolism*; D008565:Membrane Proteins; D010716:Phosphatidylinositols / Q000378:metabolism; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D027981:Symporters
chemical_list: D002352:Carrier Proteins; D006360:Heat-Shock Proteins; D007038:Hypotonic Solutions; D008565:Membrane Proteins; D010716:Phosphatidylinositols; D027981:Symporters; C073884:SLC5A3 protein, human; D007294:Inositol; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D002118:Calcium