Ca2+-secretion coupling is impaired in diabetic Goto Kakizaki rats.
The Goto Kakizaki (GK) rat is a widely used animal model to study defective glucose-stimulated insulin release in type-2 diabetes (T2D). As in T2D patients, the expression of several proteins involved in Ca(2+)-dependent exocytosis of insulin-containing large dense-core vesicles is dysregulated in this model. So far, a defect in late steps of insulin secretion could not be demonstrated. To resolve this apparent contradiction, we studied Ca(2+)-secretion coupling of healthy and GK rat beta cells in acute pancreatic tissue slices by assessing exocytosis with high time-resolution membrane capacitance measurements. We found that beta cells of GK rats respond to glucose stimulation with a normal increase in the cytosolic Ca(2+) concentration. During trains of depolarizing pulses, the secretory activity from GK rat beta cells was defective in spite of upregulated cell size and doubled voltage-activated Ca(2+) currents. In GK rat beta cells, evoked Ca(2+) entry was significantly less efficient in triggering release than in nondiabetic controls. This impairment was neither due to a decrease of functional vesicle pool sizes nor due to different kinetics of pool refilling. Strong stimulation with two successive trains of depolarizing pulses led to a prominent activity-dependent facilitation of release in GK rat beta cells, whereas secretion in controls was unaffected. Broad-spectrum inhibition of PKC sensitized Ca(2+)-dependent exocytosis, whereas it prevented the activity-dependent facilitation in GK rat beta cells. We conclude that a decrease in the sensitivity of the GK rat beta-cell to depolarization-evoked Ca(2+) influx is involved in defective glucose-stimulated insulin secretion. Furthermore, we discuss a role for constitutively increased activity of one or more PKC isoenzymes in diabetic rat beta cells.
Rose
Tobias
T
European Neuroscience Institute-Göttingen, 37073 Göttingen, Germany.
Efendic
Suad
S
Rupnik
Marjan
M
D000818:Animals; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D049108:Cell Enlargement; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D004195:Disease Models, Animal; D025802:Electric Capacitance; D004558:Electric Stimulation; D005089:Exocytosis; D005947:Glucose / Q000378:metabolism*; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D008297:Male; D008301:Maleimides / Q000494:pharmacology; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D022142:Secretory Vesicles / Q000187:drug effects / Q000378:metabolism*
D015220:Calcium Channels; D007211:Indoles; D007328:Insulin; D008301:Maleimides; D047428:Protein Kinase Inhibitors; D011493:Protein Kinase C; D005947:Glucose; C070515:bisindolylmaleimide I