title: The (Na(+)/K (+))-ATPase activity in the developing rat retina: the role of insulin-like growth factor-I (IGF-I).
abstract: In this work, the (Na(+)/K(+))-ATPase activity was evaluated during the early stages of the postnatal development of rat retina and showed an almost three-time increase from P0 to P14. Expression of the three catalytic subunit isoforms (α1, α2, and α3) of the (Na(+)/K(+))-ATPase was also evaluated by immunoblot in the same period, but no correlation to the catalytic activity increment was observed. On the other hand, immunolocalization of these three α-catalytic isoforms in the developing retina showed an age-related pattern. Involvement of IGF-I in the stimulation of the (Na(+)/K(+))-ATPase was investigated. Our results demonstrate that the exogenous IGF-I (10 ng/mL) stimulates enzyme activity at the age of P7 only. Incubation of retinas with 10 μM I-OMe-AG 538 (inhibitor of the IGF-I receptor) indicates that the basal (Na(+)/K(+))-ATPase activity is sustained by endogenous IGF-I in P7 animals. These data were corroborated by an age-dependent decrease in the immunodetection of endogenous IGF-I as well as in the phosphorylation level of its cognate receptor in rat retina homogenates. The signaling pathway involved in IGF-I-induced modulation of the (Na(+)/K(+))-ATPase was also investigated. Our data show that the inhibitory effects induced by I-OMe-AG 538 and the PI 3-kinase inhibitor Ly 294002 on the basal (Na(+)/K(+))-ATPase activity were non-cumulative. Furthermore, IGF-I induced phosphorylation of PKB in a Ly 294002-sensitive manner. Together, these data demonstrate that the PI 3-kinase/PKB signaling pathway is involved in the IGF-I-sustained basal (Na(+)/K(+))-ATPase activity during the first 7 days of the postnatal development of rat retina.
authors.affiliation: Programa de Neurociências, Instituto de Biologia, Universidade Federal Fluminense, Outeiro de São João Batista s/n, Niterói, Rio De Janeiro, CEP 24020-140, Brazil.
authors.forename: Sheila
authors.initials: S
authors.lastname: Maturana-Teixeira
authors.forename: Luis Eduardo Gomes
authors.initials: LE
authors.lastname: Braga
authors.forename: Raul
authors.initials: R
authors.lastname: Carpi Santos
authors.forename: Karin da Costa
authors.initials: Kda C
authors.lastname: Calaza
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Giestal-de-Araujo
authors.forename: Luiz Roberto
authors.initials: LR
authors.lastname: Leão-Ferreira
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D020134:Catalytic Domain; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D012160:Retina / Q000201:enzymology* / Q000254:growth & development*; D015398:Signal Transduction; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D007334:Insulin-Like Growth Factor I; D007527:Isoenzymes; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D000254:Sodium-Potassium-Exchanging ATPase