Receptor-coupled phosphoinositide hydrolysis in human retinal pigment epithelium.
Carbachol and histamine stimulated phosphoinositide (PPI) hydrolysis in cultured human retinal pigment epithelium (RPE), as reflected by an accumulation of 3H-inositol phosphates in the presence of 10 mM Li+. Carbachol increased PPI hydrolysis to greater than 600% of basal with an EC50 of 60 microM; stimulation was linear up to 60 min. This activation likely occurred via the M3 muscarinic cholinergic receptor based on the IC50 values for 4-diphenylacetoxy-N-methylpiperidine methiodide (0.47 nM), pirenzepine (280 nM), and 11-[[2-[(diethylamino)methyl]-1-piperidinyl]-acetyl]-5,11- dihydro-6H-pyrido[2,3-b][1,4]benzodiazepin-6-one (1.4 microM). Carbachol-mediated PPI hydrolysis was decreased by 80% in the absence of extracellular Ca2+. Histamine stimulated PPI turnover in a linear manner by 180% with an EC50 of 20 microM by the H1 histaminergic receptor. Serotonin, glutamate, norepinephrine, and dopamine were inactive. In human RPE, the resting cytoplasmic Ca2+ concentration, as determined by fura-2 fluorescence, was 138 +/- 24 nM. On the addition of carbachol, there was a 180% increase in peak intracellular Ca2+; addition of histamine increased intracellular Ca2+ by 187%. These results suggest receptor-mediated, inositol lipid hydrolysis is coupled to intracellular Ca2+ flux in human RPE.
Feldman
E L
EL
Department of Neurology, University of Michigan, Ann Arbor.
Randolph
A E
AE
Johnston
G C
GC
DelMonte
M A
MA
Greene
D A
DA
D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism; D006632:Histamine / Q000494:pharmacology; D006801:Humans; D006868:Hydrolysis; D009994:Osmolar Concentration; D010716:Phosphatidylinositols / Q000378:metabolism*; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism*; D011985:Receptors, Serotonin / Q000378:metabolism*; D013268:Stimulation, Chemical
D010716:Phosphatidylinositols; D011976:Receptors, Muscarinic; D011985:Receptors, Serotonin; D006632:Histamine; D002217:Carbachol; D002118:Calcium