RESUMO
We have examined the effects of ascorbate upon amino acid uptake by the in vitro toad cornea. Physiologic levels of ascorbate increase the uptake of leucine by approximately 35% but have no effect upon the uptake of alanine. Uncouplers of oxidative phosphorylation do not inhibit the stimulation by ascorbic acid of leucine accumulation, indicating the increased synthesis of ATP is not the mechanism; exogenous ATP, unlike ascorbate, stimulates the uptake of both alanine and leucine. Carbon monoxide blocks the effects of ascorbate, whereas 2-heptyl-4-hydroxyquinoline-N-oxide (HOQNO), which inhibits "reverse" electron transfer, enhances the accumulation of leucine. The evidence suggests that ascorbate serves as an energy source for the uptake of leucine.
Assuntos
Trifosfato de Adenosina/farmacologia , Aminoácidos/metabolismo , Ácido Ascórbico/farmacologia , Córnea/metabolismo , Leucina/metabolismo , 4-Hidroxiaminoquinolina-1-Óxido/farmacologia , Alanina/metabolismo , Animais , Transporte Biológico Ativo/efeitos dos fármacos , Monóxido de Carbono/farmacologia , Transporte de Elétrons/efeitos dos fármacos , Endotélio/metabolismo , Técnicas In VitroRESUMO
alpha-Aminoisobutyric acid is actively accumulated by the epithelium of the cornea of the toad, Bufo marinus, resulting in a tissue to medium ratio of 4 to 1 after 40 min of incubation. The accumulation of alpha-aminoisobutyric acid is ouabain-sensitive and dependent upon the presence of extracellular sodium. Transport is inhibited by carbon monoxide, 6-aminonicotinamide, arsenite and n-heptyl-3-hydroxy-quinoline-n-oxide and stimulated by diamide.
Assuntos
Ácidos Aminoisobutíricos/metabolismo , Córnea/metabolismo , Animais , Transporte Biológico/efeitos dos fármacos , Bufo marinus , Epitélio/metabolismo , Cinética , Ouabaína/farmacologiaRESUMO
1. Ascorbic acid, diamide and N-ethylmaleimide inhibit Na+ + K+-ATPase activity in toad corneal epithelium. 2. Ascorbic acid, diamide and N-ethylmaleimide increase alpha-aminoisobutyric acid accumulation in this tissue. 3. The effects of these compounds on corneal amino acid and ion transport are not mediated through alterations in Na+ + K+-ATPase activity.
Assuntos
Córnea/metabolismo , ATPase Trocadora de Sódio-Potássio/metabolismo , Ácidos Aminoisobutíricos/metabolismo , Animais , Ácido Ascórbico/farmacologia , Transporte Biológico/efeitos dos fármacos , Bufo marinus , Ácido Desidroascórbico/farmacologia , Diamida/farmacologia , Epitélio/efeitos dos fármacos , Epitélio/metabolismo , Etilmaleimida/farmacologia , Glutationa/análogos & derivados , Glutationa/farmacologia , Dissulfeto de Glutationa , Técnicas In VitroRESUMO
The cornea of the toad, Bufo marinus, actively transports chloride from the endothelial to the epithelial surface. This transport process has been related to the maintenance of the normal transparency of the cornea. Ion transport, as evidenced by the short-circuit current (SCC), is markedly stimulated by physiologic concentrations of ascorbic acid. Measurement of the unidirectional fluxes of 36Cl and 22Na shows that the increase in SCC is due primarily to a stimulation of the active transport of chloride.
Assuntos
Ácido Ascórbico/farmacologia , Cloretos/metabolismo , Córnea/metabolismo , Animais , Ácido Ascórbico/análogos & derivados , Transporte Biológico Ativo/efeitos dos fármacos , Bufo marinus , Córnea/fisiologia , Ácido Desidroascórbico/farmacologia , Técnicas In Vitro , Potenciais da Membrana/efeitos dos fármacos , Sódio/metabolismoRESUMO
Epithelial regeneration following scraping of a central portion of corneal epithelium of the toad, Bufo marinus, was studied. Wound closure occurred by migration of a single layer of epithelial cells from adjacent noninjured areas. Autoradiography indicated that following wound closure at two days after scraping, DNA synthesis began in these epithelial cells covering the former scraped area, and was even more pronounced three days after scraping. At four days the former denuded area was covered by an epithelium two to four cells thick and by the fifth day regeneration was complete. These studies also indicated that mitotic time in this organism is rapid.