Glucagon activates Ca2+ and Cl- channels in rat hepatocytes.
Glucagon is one of the major hormonal regulators of glucose metabolism, counteracting the hepatic effects of insulin when the concentration of glucose in the bloodstream falls below a certain level. Glucagon also regulates bile flow, hepatocellular volume and membrane potential of hepatocytes. It is clear that changes in cell volume and membrane potential cannot occur without significant ion fluxes across the plasma membrane. The effects of glucagon on membrane currents in hepatocytes, however, are not well understood. Here we show, by patch-clamping of rat hepatocytes, that glucagon activates two types of currents: a small inwardly rectifying Ca2+ current with characteristics similar to those of the store-operated Ca2+ current and a larger outwardly rectifying Cl- current similar to that activated by cell swelling. We show that the mechanism of glucagon action on membrane conductance involves phospholipase C and adenylyl cyclase. Contribution of the adenylyl cyclase-dependent pathway to activation of the currents depended on Epac (exchange protein directly activated by cAMP), but not on protein kinase A. The activation of Ca2+ and Cl- channels is likely to play a key role in the mechanisms by which glucagon regulates hepatocyte metabolism and volume.
School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia 5005, Australia.
Edoardo C
EC
Aromataris
Michael L
ML
Roberts
Greg J
GJ
Barritt
Grigori Y
GY
Rychkov
D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002478:Cells, Cultured; D065101:Chloride Channel Agonists; D018118:Chloride Channels / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D004963:Estrenes / Q000494:pharmacology; D005934:Glucagon / Q000494:pharmacology*; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology / Q000648:ultrastructure; D015640:Ion Channel Gating; D008297:Male; D018408:Patch-Clamp Techniques; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018027:Receptors, Glucagon / Q000819:agonists* / Q000378:metabolism; D013997:Time Factors; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism
D000067956:Adenylyl Cyclase Inhibitors; D002120:Calcium Channel Agonists; D015220:Calcium Channels; D065101:Chloride Channel Agonists; D018118:Chloride Channels; D002712:Chlorides; D004963:Estrenes; D047428:Protein Kinase Inhibitors; D011760:Pyrrolidinones; D018027:Receptors, Glucagon; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; C017759:9-(tetrahydro-2-furyl)-adenine; D005934:Glucagon; D000242:Cyclic AMP; D010738:Type C Phospholipases; D000262:Adenylyl Cyclases; D000225:Adenine; D002118:Calcium