My laboratory has more than thirty years of extramural funding and currently has two major projects:
- The role of H,K-ATPases in the action of aldosterone and mineralocorticoids
- The role of the Aldosterone-Endothelin System (AES) to control systemic arterial blood pressure
Our studies include experiments in conscious, unrestrained wild-type and genetically engineered mice (global and cell specific knockouts), ex vivo tissue and primary cell cultures from these animals, and well-defined cell lines. We also study the mechanism of murine and human gene regulation in immortalized and primary cell cultures.
My laboratory uses physiological, biochemical, and molecular biology techniques that include radiotelemetry, metabolic balance studies, in vitro microperfusion experiments of transepithelial net and unidirectional fluxes, single cell intracellular pH measurement, patch clamp analysis, enzymatic assays, immunoblot analysis, quantitative RT-PCR, chromatin immunoprecipitation DNA affinity purification assays, and Chromatin Accessibility by PCR Analysis (CAPA, quantitative DNase I chromatin hypersensitivity analysis).
Over the past thirty years our laboratory has contributed to the following discoveries.
We identified a novel p-type ATPase, the H,K-ATPase, in the renal collecting duct. Further studies showed that the two α subunit isoforms expressed abundantly in the stomach and colon, HKα1 and HKα2, respectively were transcriptionally competent in the renal collecting duct. Furthermore pharmacological studies demonstrated that these H,K-ATPase ion pumps were active in the collecting duct. This enzyme is important in electrolyte balance in the whole animal. Specifically, animals with a deletion of both α subunit isoform show impaired sodium and potassium balance upon mineralocorticoid stimulation.
Our laboratory demonstrated that aldosterone stimulates the transcription and the expression of endothelin-1 through direct binding of the mineralocorticoid (aldosterone) receptor to high affinity hormone response elements (HREs) in the regulatory region of the endothelin-1 gene. Disruption of the endothelin-1 gene in the collecting duct is known to increase systemic blood pressure. Our studies show that endothelin-1 peptide acts to inhibit transepithelial sodium absorption in the renal collecting duct and this action is through both the endothelin A and the endothelin B receptors. We hypothesize that this renal Aldosterone-Endothelin System exerts important feedback control to prevent excessive sodium retention in response to a high sodium intake. As a consequence, derangements in this feedback control mechanism may contribute to the development of salt-dependent hypertension.
Besides aldosterone’s effect on the endothelin-1 gene, our past research has led to the discovery of other novel aldosterone early response genes. These include the genes encoding the transcription factor and clock protein Per1 and the pro-fibrotic cytokine connective tissue growth factor.
In previous work we have shown that the renal cortical collecting duct can regulate the rate of potassium secretion independent of aldosterone. Additionally, our studies indicate that the cortical collecting duct possesses a mechanism of chloride-dependent potassium secretion.