Altered intracellular Ca2+ regulation in pancreatic acinar cells from acute streptozotocin-induced diabetic rats.
We investigated intracellular Ca2+ regulation in pancreatic acinar cells from rats with diabetes induced by a single injection of streptozotocin (80 mg/kg). Experiments were performed 2 days and 7 days after the injection of streptozotocin. The density of muscarinic receptors, measured by [3H]N-methyl scopolamine binding, was unchanged in 2-day-diabetic rats, but was significantly increased in 7-day-diabetic rats. The percentage of high affinity receptors (RH) and low affinity receptors (RL) determined from the competitive curves with [3H]N-methyl scopolamine and carbachol was not change in 2-day-diabetic rats compared to controls, whereas 7-day-diabetic rats showed a decrease in %RH and an increase in %RL. The carbachol-evoked initial peak of intracellular Ca2+ concentration ([Ca2+]i) was increased in 2-day-diabetic rats and decreased in 7-day-diabetic rats, compared to controls. In the carbachol-induced sustained phase in [Ca2+]i, the response in 7-day-diabetic rats was significantly decreased; however, there was no difference between controls and 2-day-diabetic rats. Carbachol (100 microM)-induced [3H]inositol 1,3,4-trisphosphate generation was significantly lower in diabetic rats than in the controls. The addition of inositol 1,4,5-trisphosphate (1,4,5-IP3) significantly increased 45Ca2+ release from saponin-permeabilized cells in 2-day-diabetic rats, but did not do so in 7-day-diabetic rats. Ca2+ refilling into the intracellular stores, determined by second cholecystokinin-8 (10 nM) stimulation after 10 microM carbachol stimulation, was increased in 2-day-diabetic rats and decreased in 7-day-diabetic rats. These observations indicate that the alterations in intracellular Ca2+ regulation accompanied by changes in transmembrane signaling occur in the earlier stage of the diabetic state. The findings also suggest that the increase in the carbachol-evoked [Ca2+]i peak in 2-day-diabetic rats is related predominantly to the higher sensitivity of 1,4,5-IP3-sensitive Ca2+ stores and the increase in the capacity of Ca2+ refilling in these animals, whereas the reduction in the [Ca2+]i peak in 7-day-diabetic rats appears to be related to the essential decrease in receptor-mediated 1,4,5-IP3 generation and the decrease in Ca2+ refilling capacity.
Komabayashi
T
T
Department of Pharmacology, School of Pharmacy, Tokyo University of Pharmacy and Life Science, Japan.
Sawada
H
H
Izawa
T
T
Kogo
H
H
D000208:Acute Disease; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002463:Cell Membrane Permeability / Q000187:drug effects; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D066298:In Vitro Techniques; D007293:Inosine Triphosphate / Q000378:metabolism; D008297:Male; D019832:N-Methylscopolamine; D010179:Pancreas / Q000166:cytology / Q000378:metabolism*; D010276:Parasympatholytics / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism; D012602:Scopolamine Derivatives / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D012844:Sincalide / Q000494:pharmacology
D002132:Calcium Radioisotopes; D010276:Parasympatholytics; D010716:Phosphatidylinositols; D011976:Receptors, Muscarinic; D012602:Scopolamine Derivatives; D007293:Inosine Triphosphate; D012844:Sincalide; D002118:Calcium; D019832:N-Methylscopolamine