|Birkenkamp-Demtroeder K et al.|
Expression of Water Channels in the Human Heart
Journal of Clinical and Basic Cardiology 2003; 6 (1-4): 77-79
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Keywords: Aquapore, Blutfluss, Herz, Kardiologie, Wasserkanal, Aquaporin, blood flow, cardiology, heart, water channel
Myocardial blood flow and oxidative metabolism are heterogeneous. Both measures correlate significantly in the normoxic myocardium. We assume that in high flow areas with high metabolism, water channels (aquaporins; AQPs) secure transport of the respiratory water through membranes. Thus, high metabolism areas should express high AQP levels and vice versa. We investigated AQP1 and AQP4 – that are not well defined in the human myocardium – in normoxic and postischaemic/reperfused rabbit hearts, in intact human atria, and in human hearts with dilatative cardiomyopathy (DCM). The existence of both AQPs was assessed on the mRNA level, the protein level, and by using immunohistochemistry. AQP1 mRNA is heterogeneously expressed in the rabbit heart and the human heart. The expression and the heterogeneity are reduced in impaired hearts (postischaemic rabbit hearts and DCM hearts) compared with the expression and the heterogeneity in normoxic rabbit hearts and in intact human atrium. The AQP1 protein is also heterogeneously distributed in the myocardium. However, the protein expression in the left ventricles of the DCM hearts is not reduced in parallel with the mRNA expression. We attribute the low left ventricular values to a loss of heterogeneity in metabolism in these hearts. In addition, we provide the first direct evidence of AQP4 mRNA expression in normoxic rabbit hearts and in DCM hearts. Moreover, we show a different pattern between the AQP1 and the AQP4 proteins in the rabbit myocardium. AQP1 appeared as randomly distributed points and AQP4 had a garland-like appearance reminding one of the distribution of capillaries and the contour of cardiomyocytes, respectively. We suggest that AQP1 is responsible to transport water through the capillary endothelium, and that AQP4 facilitates the water transport across cardiomyocyte membranes.