RESUMEN
BACKGROUND/AIMS: Although aquaglyceroporins have been generally believed to operate in a channel mode, which is of nonsaturable nature, for glycerol as well as for water, we recently found that human aquaporin 9 (hAQP9) operates in a carrier-mediated mode, which is of saturable nature, for glycerol. Based on the finding, we assumed that such a characteristic might be shared by the other aquaglyceroporins and examined the functional characteristics of hAQP10, which is an intestine-specific aquaglyceroporin. METHODS: Transport assays were conducted using Xenopus laevis oocytes expressing hAQP10 derived from the microinjected cRNA. RESULTS: The transport of glycerol by hAQP10 was found to be highly saturable with a Michaelis constant of 10.4 µM and specifically inhibited by several glycerol analogs such as monoacetin. Furthermore, when glycerol was preloaded in hAQP10-expressing oocytes, its efflux was trans-stimulated by extracellular glycerol. These results indicate the involvement of a carrier-mediated mechanism in glycerol transport by hAQP10. Interestingly, a channel mechanism was also found to be involved in part in hAQP10-mediated glycerol transport. CONCLUSION: The present study unveiled the uniquely dual functional characteristic of hAQP10 as a carrier/channel for solute transport, providing a novel insight into its operation mechanism, which would help further elucidate its physiological role.
Asunto(s)
Acuaporinas/fisiología , Animales , Acuaporinas/genética , Secuencia de Bases , Transporte Biológico , Cartilla de ADN , ADN Complementario , Femenino , Glicerol/metabolismo , Humanos , Cinética , Xenopus laevisRESUMEN
Melanogenesis is the physiological process by which melanin is synthesized to protect the skin from UV damage. While paracrine interactions between keratinocytes and melanocytes are crucial for regulating epidermal pigmentation, the endothelin (EDN)-endothelin B-receptor (EDNRB) interaction is one of the key linkages. In this study, we found that a single exposure of normal human melanocytes (NHMs) with UVB stimulates the expression of EDNRB and its upstream transcription factor microphthalmia-associated transcription factor (MITF) at the transcriptional and translational levels. That stimulation can be abrogated by post-irradiation treatment with a French maritime pine bark extract (PBE). UVB stimulated the phosphorylation of p38 and c-jun N-terminal kinase (JNK), but not ERK, followed by the increased phosphorylation of MSK1 and CREB. The post-irradiation treatment with PBE did not affect the increased phosphorylation of p38 and JNK, but distinctly abrogated the phosphorylation of MSK1 and CREB. Post-irradiation treatment with the MSK1 inhibitor H89 significantly down-regulated the increased gene expression of MITF and EDNRB in UVB-exposed NHMs. Our findings indicate for the first time that the increased expression of MITF that leads to the up-regulation of melanocyte-specific proteins in UVB-exposed NHMs is mediated via activation of the p38/MSK1/CREB pathway but not the ERK/RSK/CREB pathway. The mode of action by PBE demonstrates that interrupting MSK1 activation is a new target for antioxidants including PBE which can serve as anti-pigmenting agents in a reactive oxygen species-depletion-independent manner.
Asunto(s)
Melanocitos/efectos de los fármacos , Pinus/química , Extractos Vegetales/farmacología , Receptor de Endotelina B/genética , Proteínas Quinasas S6 Ribosómicas 90-kDa/genética , Transducción de Señal/efectos de los fármacos , Rayos Ultravioleta/efectos adversos , Células Cultivadas , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/genética , Endotelinas/efectos de los fármacos , Endotelinas/genética , Expresión Génica/efectos de los fármacos , Expresión Génica/genética , Humanos , Proteínas Quinasas JNK Activadas por Mitógenos/genética , Queratinocitos/efectos de los fármacos , Melaninas/genética , Melanocitos/metabolismo , Factor de Transcripción Asociado a Microftalmía/genética , Fosforilación/efectos de los fármacos , Fosforilación/genética , Pigmentación/efectos de los fármacos , Pigmentación/genética , Corteza de la Planta/química , Transducción de Señal/genética , Piel/efectos de los fármacos , Regulación hacia Arriba/efectos de los fármacos , Regulación hacia Arriba/genética , Proteínas Quinasas p38 Activadas por Mitógenos/genéticaRESUMEN
When we recognize a sensory event, we experience a confident feeling that we certainly know the perceived world 'here and now'. However, it is unknown how and where the brain generates such 'perceptual confidence'. Here we found neural correlates of confidence in the primate pulvinar, a visual thalamic nucleus that has been expanding markedly through evolution. During a categorization task, the majority of pulvinar responses did not correlate with any 'perceptual content'. During an opt-out task, pulvinar responses decreased when monkeys chose 'escape' options, suggesting less confidence in their perceptual categorization. Functional silencing of the pulvinar increased monkeys' escape choices in the opt-out task without affecting categorization performance; this effect was specific to the contralateral visual target. These data were supported by a theoretical model of confidence, indicating that pulvinar activities encode a subject's certainty of visual categorization and contribute to perceptual confidence.