Rapid nongenomic effects of 3,5,3'-triiodo-L-thyronine on the intracellular pH of L-6 myoblasts are mediated by intracellular calcium mobilization and kinase pathways.
L-T3 and L-T4 activated the Na+/H+ exchanger of L-6 myoblasts, with a fast nongenomic mechanism, both in the steady state and when cells undergo acid loading with ammonium chloride. Monitored with the intracellular pH-sensitive fluorescent probe 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein, activation of the exchanger appeared to be initiated at the plasma membrane, because T3-agarose reproduced the effect of L-T3, and triiodothyroacetic acid, a hormone analog previously shown to inhibit membrane actions of thyroid hormone, blocked the action of L-T3 on the exchanger. We show here for the first time that transduction of the hormone signal in this nongenomic response requires tyrosine kinase-dependent phospholipase C activation and two different signaling pathways: 1) mobilization of intracellular calcium, assessed by the fluorescent probe fura-2, through activation of inositol trisphosphate receptors and without contributions from extracellular calcium or ryanodine receptors; and 2) protein phosphorylation involving protein kinase C and MAPK (ERK1/2), as shown by the use of kinase inhibitors and by immunoblotting for activated kinases.
D'Arezzo
Silvia
S
Department of Biology, University of Rome Roma Tre, 00146 Roma, Italy.
Incerpi
Sandra
S
Davis
Faith B
FB
Acconcia
Filippo
F
Marino
Maria
M
Farias
Ricardo N
RN
Davis
Paul J
PJ
D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration / Q000187:drug effects*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology; D032446:Myoblasts / Q000187:drug effects / Q000201:enzymology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D014284:Triiodothyronine / Q000494:pharmacology*
D000889:Anti-Arrhythmia Agents; D004791:Enzyme Inhibitors; D017923:Sodium-Hydrogen Exchangers; D014284:Triiodothyronine; D000584:Amiloride; D011493:Protein Kinase C; D002118:Calcium; C039614:ethylisopropylamiloride