The central hypothesis of this project is that cytosolic free calcium concentration (Cai) is the major regulator of aldosterone biosynthesis and secretion. In the first grant period, investigation of Cai in adrenal zona glomerulosa (ZG) was extended to the single cell level. These studies precisely quantitated the extent of Cai changes that occur during secretagogue stimulation. Elevation of extracellular K+ in its physiological range produces a sustained rise in Cai that is probably a consequence of the activation of voltage-dependent Ca2+ channels. On the other hand, the Cai response to angiotensin II (AngII) exhibits a spatially non-uniform and temporally oscillating pattern. Despite the complexity of the Cai responses, our results from parallel studies comparing the temporal characteristics of aldosterone secretion and Cai have further strengthen the Ca2+ hypothesis for aldosterone regulation. The experiments in the present proposal will employ single cell Cai measurement and plasma membrane, patch-clamp electrophysiology to address the following Specific Aims: (1) To determine if cytosolic Ca2+ mobilization mechanisms underlie the oscillatory pattern of ZG cell Cai stimulated by AngII. (2) To determine the role of plasma membrane potential and voltage- and receptor operated ion channels in controlling or modulating the Cai oscillations. (3) To investigate the mechanisms responsible for the restoration of Cai to basal levels following a stimulated rise. Abnormal regulation of aldosterone secretion has been reported in a substantial fraction of the hypertensive population, particularly in response to AngII infusion. The mechanisms responsible for these alterations in hormonal secretion are unknown. We have recently documented that ZG cells from the spontaneously hypertensive rat (SHR) have an elevated resting Cai and a blunted calcium response to AngII and K+ application, suggesting that a sustained increase in Cai may be casually related to the altered steroid response to secretagogues. These findings provide the basis for the last Specific Aim: (4) To test the hypothesis that the pathophysiological consequences of the hypertensive state result, in part, from effects on basal and secretagogue-modified Cai levels in single ZG cells.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK040127-05
Application #
3240230
Study Section
General Medicine B Study Section (GMB)
Project Start
1988-05-01
Project End
1996-04-30
Budget Start
1992-05-01
Budget End
1993-04-30
Support Year
5
Fiscal Year
1992
Total Cost
Indirect Cost
Name
Boston University
Department
Type
Schools of Medicine
DUNS #
604483045
City
Boston
State
MA
Country
United States
Zip Code
02118
Jimenez, C; Gireldez, F; Represa, J et al. (1997) Calcium currents in dissociated cochlear neurons from the chick embryo and their modification by neurotrophin-3. Neuroscience 77:673-82
Cheung, J Y; Zhang, X Q; Bokvist, K et al. (1997) Modulation of calcium channels in human erythroblasts by erythropoietin. Blood 89:92-100
Shepherd, R M; Williams, G H; Quinn, S J (1992) Regulation of intracellular pH in single rat zona glomerulosa cells. Am J Physiol 262:C182-90
Kanazirska, M V; Vassilev, P M; Quinn, S J et al. (1992) Single K+ channels in adrenal zona glomerulosa cells. II. Inhibition by angiotensin II. Am J Physiol 263:E760-5
Vassilev, P M; Kanazirska, M V; Quinn, S J et al. (1992) K+ channels in adrenal zona glomerulosa cells. I. Characterization of distinct channel types. Am J Physiol 263:E752-9
Waybill, M M; Yelamarty, R V; Zhang, Y L et al. (1991) Nuclear calcium gradients in cultured rat hepatocytes. Am J Physiol 261:E49-57
Brauneis, U; Vassilev, P M; Quinn, S J et al. (1991) ANG II blocks potassium currents in zona glomerulosa cells from rat, bovine, and human adrenals. Am J Physiol 260:E772-9
Longo, E A; Tornheim, K; Deeney, J T et al. (1991) Oscillations in cytosolic free Ca2+, oxygen consumption, and insulin secretion in glucose-stimulated rat pancreatic islets. J Biol Chem 266:9314-9
Quinn, S J; Enyedi, P; Tillotson, D L et al. (1991) Kinetics of cytosolic calcium and aldosterone responses in rat adrenal glomerulosa cells. Endocrinology 129:2431-41
Yelamarty, R V; Miller, B A; Scaduto Jr, R C et al. (1990) Three-dimensional intracellular calcium gradients in single human burst-forming units-erythroid-derived erythroblasts induced by erythropoietin. J Clin Invest 85:1799-809