Cardiac aquaporin expression in humans, rats, and mice

1 Kids Heart Research; 2 Neurogenetics Research Unit and Institute for Neuromuscular Research, Children’s Hospital at Westmead; 3 Discipline of Pediatrics and Child Health, Faculty of Medicine, University of Sydney, Sydney, New South Wales, Australia; 4 Departments of Medicine and Physiology, Cardiovascular Research Institute, University of California, San Francisco, California; and 5 Muscle Development Unit, Children’s Medical Research Institute, Sydney, New South Wales, Australia Submitted 23 January 2006 ; accepted in final form 3 March 2006 Water accumulation in the heart is important in ischemia-reperfusion injury and operations performed by using cardiopulmonary bypass, with cardiac dysfunction associated with myocardial edema being the principal determinant of clinical outcome. As an initial step in determining the role of aquaporin (AQP) water channels in myocardial edema, we have assessed the myocardial expression of AQPs in humans, rats, and mice. RT-PCR revealed expression of AQP-1, -4, -6, -7, -8, and -11 transcripts in the mouse heart. AQP-1, -6, -7, and -11 mRNAs were found in the rat heart as well as low levels of AQP-4 and -9. Human hearts contained AQP-1, -3, -4, -5, -7, -9, -10, and -11 mRNAs. AQP-1 protein expression was confirmed by Western blot analysis in all three species. AQP-4 protein was detected in the mouse heart but not in the rat or human heart. To determine the potential functional consequences of myocardial AQP expression, water permeability was measured in plasma membrane vesicles from myocardial cells of wild-type versus various AQP knockout mice. Water permeability was reduced by AQP-1 knockout but not by AQP-4 or AQP-8 knockout. With the use of a model of isolated rat heart perfusion, it was found that osmotic and ischemic stresses are not associated with changes in AQP-1 or AQP-4 expression. These studies support a possible functional role of AQP-1 in myocardium but indicate that early adaptations to osmotic and ischemic stress do not involve transcriptional or posttranslational AQP-1 regulation. aquaporin knockout; cardiac myocyte; cardiopulmonary bypass Address for reprint requests and other correspondence: D. Winlaw, Kids Heart Research, Children’s Hospital at Westmead, Locked Bag 4001, Westmead, NSW 2145, Australia (e-mail: davidw{at}chw.edu.au )