RESUMO
Five sesquiterpene alcohol esters of the carotane series, from plants of the genus Ferula, were investigated with regard to their capacity to modify the ion permeability of both planar lipid bilayers and mitochondria. These compounds are subdivided into two structural groups that differ in their effects on membrane permeability. Complex esters of sesquiterpene alcohols with aliphatic acids, which constituted the first group (lapidin and lapiferin), do not possess ionophoric properties. The second group comprised complex esters of sesquiterpene alcohols with aromatic acids (ferutinin, tenuferidin and ferutidin), all of which increase cation permeability of lipid bilayers and mitochondria in a dose-dependent manner. A pronounced selectivity of the terpenoid-modified membranes for divalent cations versus monovalent cations was found. Evidence of a carrier mechanism for terpenoid-induced ion transport is demonstrated. A tentative complex composed of a divalent cation with two molecules of membrane-active terpenoid is proposed.
Assuntos
Membranas Intracelulares/efeitos dos fármacos , Ionóforos/farmacologia , Bicamadas Lipídicas/química , Terpenos/farmacologia , Animais , Benzoatos/farmacologia , Compostos Bicíclicos com Pontes , Cicloeptanos , Eletroquímica , Membranas Intracelulares/química , Transporte de Íons , Mitocôndrias Hepáticas/efeitos dos fármacos , Modelos Moleculares , Estrutura Molecular , Permeabilidade , Plantas/química , Ratos , Sesquiterpenos/farmacologia , Relação Estrutura-Atividade , Terpenos/químicaRESUMO
To examine the extracellular Na(+) sensitivity of a renal inwardly rectifying K(+) channel, we performed electrophysiological experiments on Xenopus oocytes or a human kidney cell line, HEK293, in which we had expressed the cloned renal K(+) channel, ROMK1 (Kir1. 1). When extracellular Na(+) was removed, the whole-cell ROMK1 currents were markedly suppressed in both the oocytes and HEK293 cells. Single-channel ROMK1 activities recorded in the cell-attached patch on the oocyte were not affected by removal of Na(+) from the pipette solution. However, macro-patch ROMK1 currents recorded on the oocyte were significantly suppressed by Na(+) removal from the bath solution. A blocker of Na(+)/H(+) antiporters, amiloride, largely inhibited the Na(+) removal-induced suppression of whole-cell ROMK1 currents in the oocytes. The pH-insensitive K80M mutant of ROMK1 was much less sensitive to Na(+) removal. Na(+) removal was found to induce a significant decrease in intracellular pH in the oocytes using H(+)-selective microelectrodes. Coexpression of ROMK1 with NHE3, which is a Na(+)/H(+) antiporter isoform of the kidney apical membrane, conferred increased sensitivity of ROMK1 channels to extracellular Na(+) in both the oocytes and HEK293 cells. Thus, it is concluded that the ROMK1 channel is regulated indirectly by extracellular Na(+), and that the interaction between NHE transporter and ROMK1 channel appears to be involved in the mechanism of Na(+) sensitivity of ROMK1 channel via regulating intracellular pH.
Assuntos
Canais de Potássio Corretores do Fluxo de Internalização , Canais de Potássio/metabolismo , Trocadores de Sódio-Hidrogênio/metabolismo , Sódio/metabolismo , Animais , Linhagem Celular , Feminino , Humanos , Técnicas In Vitro , Oócitos/efeitos dos fármacos , Oócitos/metabolismo , Técnicas de Patch-Clamp , Canais de Potássio/efeitos dos fármacos , Canais de Potássio/genética , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Sódio/farmacologia , XenopusRESUMO
A component capable of modifying bilayer phospholipid membranes (BPM) with the formation of conductivity channels was found in the fraction cytoplasmic proteins of the rat liver. Cation-anionic selectivity of channels depending on medium pH and cation type was studied. Current voltage characteristics of single channel is extremely asymmetric. It is suggested that the studied factor is a cytoplasmic regulator of the permeability of membrane structure in the cell.
