Our long-term objective is to develop an understanding of the physiological functions of a broad array of ion transporters that maintain acid-base, electrolyte, and Ca homeostasis in cardiovascular and pulmonary tissues in vivo. These include at least 8 HCO3 transporters, the NHE1 Na/H exchanger, the NKCC1 Na-K-2CI cotransporter, and at least 7 Ca pumps. With few exceptions, the activities of specific isoforms cannot be distinguished in vivo or in vitro. To understand the physiological role and relative importance of each transporter, we are systematically developing and analyzing gene-targeted and transgenic mouse models. We have already developed many of these models, and have identified phenotypes involving cardiac performance, ischemic-reperfusion injury, blood pressure, vascular and airway smooth muscle tone, airway anion secretion, and others.
In Aim 1 we will develop knockout mice for both Na-HCO3 cotransporters and Ca pumps and transgenic mice that allow rescue of severe phenotypes for the AE1 and AE2 CI/HCO3 exchangers and NHE1 Na/H exchanger knockouts.
In Aim 2 we will determine the physiological consequences of transporter dysfunction in cardiovascular tissues and lung. Specifically, we will analyze: a) cardiac function to determine whether, and to what extent, the null mutations affect cardiac performance and alter responses to ischemic-reperfusion injury and hypertrophic stimuli, b) blood pressure at the whole animal level and vascular smooth muscle contractility and ion homeostasis at the tissue level, c) pulmonary function in mechanically ventilated mice under normal conditions and following bronchoconstrictor challenge, and d) ion transport mechanisms involved in transepithelial anion currents and smooth muscle tone in isolated airway preparations. These studies will test the hypotheses that the acid-base, electrolyte, and Ca transporters being studied regulate cardiac contractility and pulmonary and vascular smooth muscle tone and contractility, which in turn affect cardiac function in health and disease, arterial blood pressure, and airway resistance. We anticipate that the new mouse lines being developed in this proposal will, like the models already developed, become valuable models for analysis of the mechanisms by which these ion transporters regulate the physiological functions of cardiovascular, pulmonary, and other tissues. ? ?
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