This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Hypertension is a chronic condition associated with increased risk of mortality and morbidity from stroke, coronary heart disease, congestive heart failure, and chronic renal disease. Difficulty in controlling hypertension is due, in part, to the complexity of the pathophysiology of hypertension. In addition to the involvement of multiple pathways and feedback mechanisms, hypertension is often associated with other pathological conditions such as renal dysfunction, which is tightly linked to the renin-angiotensin system (RAS). Angiotensin (AngII), an important regulator of RAS, plays a critical role in regulation of blood pressure and volume homeostasis. These effects are mediated mainly via Ca2+ mobilization. Investigators reported the involvement of sphingosine kinase1 (SK1) in the mobilization of intracellular Ca2+. However, the exact mechanism is poorly understood. Here, we tested whether SK1 plays a role in AngII-stimulated Ca2+ release and regulating vascular tone. Our early observation using FLIPR to measure the intracellular Ca2+ levels indicated a characteristic pattern of AngII induced increase in intracellular Ca2+ level, an immediate peak followed by a sustained Ca2+ release. Additionally, selective inhibition of EGFR by AG1478 or the SK1 inhibitor, (DMS) inhibited the second phase. Also, AngII and EGF increased endogenous SK1 activity and enhanced production of S1P. Deletion of SK1 or DMS treatment abrogated EGF-induced intracellular Ca2+ elevation. Moreover, perfusion of the arteriole of the isolated rabbit glomerular structure with either AG1478 or DMS blocked the sustained elevation of intracellular Ca2+ and pressor response of Ang II. In vivo experiments performed on wild type and SK1-/- mice revealed that deletion of SK1 reverses the effect of AngII on GFR. Based on our data we propose to elucidate the role of EGFR transactivation and SK1/S1P in AngII-dependent intracellular Ca2+ mobilization, vascular tone, and renal hemodynamics. This study will enable us to gain important insight into the pathophysiology of hypertension and may provide novel therapeutic interventions.