Expression Of aquaporin-1 (AQP-1) in rat heart

Abstract

Background. AQP-1, a channel-forming integral membrane protein of 28 kDa prevalent in red blood cells and renal proximal tubules, was recently shown to be expressed in rat heart. Aims: Our purpose was to charaterise the experssion of the AQO-1 gene in rat heart with respect to cell type, developmental stage and pathophysiological condition. Methods: To determine in which heart cell type the water channel was expressed, we measured AQP-1 mRNA and protein levels and immunolocalised protein in freshly isolated myocytes from adult rats and cultured myocytes and fibroblasts from neonatal rats. Results: Northern blot analysis showed that AQP-1 mRNA is expressed in adult cardiac myocytes, neonatal myocytes, and neonatal cardiac fibroblasts of rats at levels nearly as high as those observed in rat kidney. Western blot analysis, however, detected AQP-1 protein only in purified adult and neonatal cardiac myocytes at levels markedly less than kidney. Immunohistochemistry and confocal imaging localised AQP-1 protein to the sarcolemmal membrane of myocytes. Since the expression of other membrane-spanning proteins is altered during hypertrophy, we determined the level of AQP-1 mRNA in hearts of aortic-constricted (AC) rats. The level of AQP-1 mRNA decreased progressively after AC, and was 42% less than the level in left ventricles (LVs) of sham-operated control rats after 3 days of AC. Conclusions: These data indicate that AQP-1 is expressed in cardiac myocytes of adult and neonatal rats, and its expression is modulated in the rat heart during pressure-overload hypertrophy.