Effect of glucagon on intracellular pH regulation in isolated rat hepatocyte couplets
Alvaro, D.; Della Guardia, P.; Bini, A.; Gigliozzi, A.; Furfaro, S.; La Rosa, T.; Piat, C.; Capocaccia, L.
Journal of Clinical Investigation 96(2): 665-675
ISSN/ISBN: 0021-9738 PMID: 7635959 Accession: 008532942
To elucidate mechanisms of glucagon-induced bicarbonate-rich choleresis, we investigated the effect of glucagon on ion transport processes involved in the regulation of intracellular pH (pH-i) in isolated rat hepatocyte couplets. It was found that glucagon (200 nM), without influencing resting pH-i, significantly stimulates the Cl-/HCO-3- exchange activity. The effect of glucagon was associated with a sevenfold increase in cAMP levels in rat hepatocytes. The activity of the Cl-/HCO-3- exchanger was also stimulated by DBcAMP + forskolin. The effect of glucagon on the Cl-/HCO-3- exchange was individually blocked by two specific and selective inhibitors of protein kinase A, Rp-cAMPS (10 mu-M) and H-89 (30 mu-M), the latter having no influence on the glucagon-induced cAMP accumulation in isolated rat hepatocytes. The Cl- channel blocker, NPPB (10 mu-M), showed no effect on either the basal or the glucagon-stimulated Cl-/HCO-3- exchange. In contrast, the protein kinase C agonist, PMA (10 mu-M), completely blocked the glucagon stimulation of the Cl-/HCO-3- exchange; however, this effect was achieved through a significant inhibition of the glucagon-stimulated cAMP accumulation in rat hepatocytes. Colchicine pretreatment inhibited the basal as well as the glucagon-stimulated Cl-/HCO-3- exchange activity. The Na+/H+ exchanger was unaffected by glucagon either at basal pH-i or at acid pH-i values. In contrast, glucagon, at basal pH-i, stimulated the Na+-HCO-3- symport. The main findings of this study indicate that glucagon, through the cAMP-dependent protein kinase A pathway, stimulates the activity of the Cl-/HCO-3- exchanger in isolated rat hepatocyte couplets, a mechanism which could account for the in vivo induced bicarbonate-rich choleresis.