Alpha 2-adrenergic stimulation counteracts glucose-induced rise of sodium in pancreatic islets exposed to ouabain.
The effects of alpha 2-adrenergic activation by clonidine on sodium handling were analysed in beta-cell-rich pancreatic mouse islets. In the steady-state situation, clonidine (1 microM) amplified lowering of sodium induced by 20 mM glucose, while the content remained unchanged in 3mM glucose. The loss of sodium in Na(+)-deficient medium was stimulated by glucose but was not affected by clonidine. This agonist also did not influence the ouabain-induced uptake of sodium at 3 mM glucose but partially counteracted additional uptake in response to 20 mM glucose. Although lacking effects of its own, 5 microM yohimbine completely counteracted the action of clonidine. The glucose amplification of the ouabain-induced uptake of sodium was suppressed also by 10 microM of the Ca(2+)-channel blockers methoxyverapamil and diltiazem. Both tolbutamide (100 microM) and dibutyryl cyclic AMP (1 mM) mimicked the action of glucose by promoting clonidine-sensitive uptake of sodium in the presence of ouabain. It is concluded that activation of alpha 2-adrenoceptors has profound effects on the sodium handling of pancreatic beta-cells exposed to glucose and other stimulators of insulin release.
Saha
S
S
Department of Medical Cell Biology, University of Uppsala, Sweden.
Hellman
B
B
D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003000:Clonidine / Q000494:pharmacology*; D004110:Diltiazem / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005711:Gallopamil / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology*; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008820:Mice, Obese; D012964:Sodium / Q000378:metabolism*; D014044:Tolbutamide / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D002121:Calcium Channel Blockers; D015016:Yohimbine; D005711:Gallopamil; D003994:Bucladesine; D014044:Tolbutamide; D012964:Sodium; D004110:Diltiazem; D005947:Glucose; D003000:Clonidine