These studies will identify the effect and characterize the mechanism of adrenergic agents on sodium transport in the distal convoluted tubule. The unifying hypothesis of the proposal is that activation of adrenergic receptors on distal convoluted tubules stimulates sodium transport. Activation of renal adrenergic receptors by nerve stimulation or circulating catecholamines increases sodium reabsorption. While a number of studies have examined adrenergic regulation in other nephron segments, the effects of these receptors on sodium transport in the distal convoluted tubule have been difficult to identify due to its short length and inaccessibility. Although the bulk of sodium reabsorption occurs in the proximal nephron, a critical role in the fine adjustment of sodium reabsorption has been attributed to the distal convoluted tubule. Experiments will be performed on immortalized distal convoluted tubule cells. These immortalized cells, that have been developed and characterized in this laboratory, express functional alpha and Beta adrenergic receptors and sodium transport pathways identical to those in distal convoluted tubules. Preliminary data indicate that alpha2 but not alpha1 adrenergic receptors stimulate sodium influx into these cells through electrogenic sodium channels and electroneutral sodium chloride cotransport mechanisms. Pilot studies also show that alpha2 receptor stimulation decrease intracellular sodium and increase Na-K-ATPase activity in these cells. The experiments described in this proposal will test hypotheses related to: 1) characterizing the membrane pathways mediating sodium influx following alpha2 receptor activation; 2) determining if alpha2 adrenergic receptors stimulate sodium transport in distal convoluted tubule cells secondary to activation of Na-K-ATPase; 3) protein kinase C dependence and second messenger pathways utilized by alpha2 receptors; 4) characterizing the relations between intracellular calcium and activation of Na-K-ATPase; and, 5) determining the effect of Beta adrenergic activation on sodium transport in distal convoluted tubule cells. The methods to be used include isotopic flux experiments, fluorescent dyes to measure intracellular sodium, calcium and membrane voltage, and biochemical analyses of intracellular second messengers. The results of this work will provide important information regarding adrenergic regulation of sodium transport in the distal convoluted tubule, the cellular mechanisms and signaling pathways utilized to mediate these effects. The characterization of adrenergic regulation in this segment is particularly important because alpha2 adrenergic receptors may be involved in the pathogenesis of hypertension and a number of adrenergic drugs are currently used as primary agents in the treatment of hypertension. Elucidation of the mechanisms invoked by adrenergic receptors may provide the basis for selective drug design and choices in treatment.
| Gesek, F A (1993) Stimulation of alpha 2-adrenergic receptors increases Na(+)-K(+)-ATPase activity in distal convoluted tubule cells. Am J Physiol 265:F561-8 |
