Intracellular and plasma membrane-initiated pathways involved in the [Ca^sup 2+^]^sub i^ elevations induced by iodothyronines (T3 and T2) in pituitary GH^sub 3^ cells

The role of 3,5,3'-triiodo-l-thyronine (T3) and its metabolite 3,5-diiodo-l-thyronine (T2) in modulating the intracellular Ca... concentration ([Ca...]...) and endogenous nitric oxide (NO) synthesis was evaluated in pituitary GH3 cells in the absence or presence of extracellular Ca... When applied in Ca...-free solution, T2 and T3 increased [Ca...]i, in a dose-dependent way, and NO levels. Inhibition of neuronal NO synthase by N...-nitro-l-arginine methyl ester and l-n...-(1-iminoethyl)ornithine hydrochloride significantly reduced the [Ca...]... increase induced by T2 and T3. However, while depletion of inositol trisphosphate-dependent Ca... stores did not interfere with the T2- and T3-induced [Ca...]... increases, the inhibition of phosphatidylinositol 3-kinase by LY-294002 and the dominant negative form of Akt mutated at the ATP binding site prevented these effects. Furthermore, the mitochondrial protonophore carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone prevented the increases in both [Ca...]... and NO elicited by T2 or T3. Interestingly, rotenone blocked the early [Ca...]... increases elicited by T2 and T3, while antimycin prevented only that elicited by T3. Inhibition of mitochondrial Na+/Ca... exchanger by CGP37157 significantly reduced the [Ca...]... increases induced by T2 and T3. In the presence of extracellular calcium (1.2 mM), under carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone, T2 and T3 increased both [Ca...]... and intracellular Na+ concentration; nimodipine reduced the [Ca...]... increases elicited by T2 and T3, but inhibition of NO synthase and blockade of the Na+/H+ pump by 5-(N-ethyl-N-isopropyl)amiloride prevented only that elicited by T3; and CB-DMB, bisindolylmaleimide, and LY-294002 (inhibitors of the Na+/Ca... exchanger, PKC, and phosphatidylinositol 3-kinase, respectively) failed to modify the T2- and T3-induced effects. Collectively, the present results suggest that T2 and T3 exert short-term nongenomic effects on intracellular calcium and NO by modulating plasma membrane and mitochondrial pathways that differ between these iodothyronines. (ProQuest: ... denotes formulae/symbols omitted.)