Introduction. The NaCl cotransporter (NCC) is expressed in the kidney distal convoluted tubule (DCT) and is a widely used pharmacological target for hypertension treatment. NCC is also important for plasma potassium (K⁺) homeostasis, as changes in NCC activity can influence the degree of electrogenic K⁺ secretion in the latter portions of the renal tubule. Changes in NCC phosphorylation track with NCC activity, with greater NCC phosphorylation correlating with higher NCC activity. Phosphorylation of NCC is increased in response to various stimuli, including changes in the extracellular K⁺ concentration, or after alterations in intracellular cAMP following vasopressin or adrenergic hormone stimulation of GPCRs. Database searching indicated that the GαS coupled glucagon receptor (GluR), which also signals via cAMP, was abundantly expressed in the DCT. We hypothesized that glucagon was a potent modulator of NCC activity, Na⁺ and K⁺ balance and ultimately blood pressure.

Methods. Ex vivo effects of glucagon on NCC phosphorylation status were assessed in mouse and human tissue. Involvement of selective signaling pathways downstream of the GluR were determined using pharmacological tools. In vivo effects of short-term or long-term glucagon administration on blood pressure, and Na⁺ and K⁺ balance was examined in mice. 

Results. In mice, 30-min glucagon exposure increased NCC phosphorylation.  In ex vivo kidney tubule suspensions glucagon increased NCC phosphorylation in a time and dose-dependent manner, an effect prevented by a GluR inhibitor. Glucagon increased NCC phosphorylation in human kidney slices. Selective pharmacological inhibition of adenylyl cyclase, protein kinase A, with no lysine kinases (WNK) and inward-rectifier potassium channels 4.1/5.1 or intracellular Ca²⁺ chelation antagonized the effects of glucagon on NCC phosphorylation. Glucagon effects were absent in tubules isolated from protein phosphatase 1 inhibitor-1 KO mice. In mice administered glucagon by osmotic mini-pump for 14 days, plasma glucagon was significantly higher and NCC phosphorylation 2-fold greater than the vehicle group. Plasma Na⁺ and K⁺ levels were not significantly different between groups. Despite the increase in NCC phosphorylation, preliminary studies suggest that glucagon prevents the ability of a high NaCl intake to increase blood pressure.

Conclusion. Glucagon is a potent stimulator of NCC phosphorylation and activity. The actions of glucagon in modulating electrolyte balance and blood pressure may be underappreciated and play an important role in human physiology/pathophysiology.