Mobilization of 45Ca from insulin-producing RINm5F cells attached to microcarriers.
A technique was designed allowing studies of 45Ca efflux from insulin-releasing cells of a clonal cell line (RINm5F) attached to fibronectin-coated plastic beads. Supporting the existence of Ca2+-Ca2+ and Na+-Ca2+ exchange mechanisms, the efflux of 45Ca in a Ca2+-deficient perifusion medium was increased after introduction of Ca2+ and decreased after removal of Na+. The washout of radioactivity was similar to that from pancreatic islets in also being inhibited by glucose in the presence of low concentrations of extracellular Ca2+. During perifusion with a medium containing 2.56 mM Ca2+, increasing the K+ concentration resulted in an increased 45Ca efflux, a process counteracted by D-600. Also, exposure to tolbutamide resulted in a distinct stimulatory peak. Glucose was a poor stimulator of 45Ca efflux, suggesting that this sugar lacks the ability to depolarize the RINm5F cells sufficiently to induce normal opening of the voltage-dependent channels in the plasma membrane. Such a defect might well explain why the RINm5F cells do not respond to glucose with stimulation of insulin release.
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002132:Calcium Radioisotopes; D002999:Clone Cells; D003584:Cytological Techniques; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000096:biosynthesis*; D007515:Islets of Langerhans; D010190:Pancreatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000494:pharmacology
D002132:Calcium Radioisotopes; D007328:Insulin; D012964:Sodium; D005947:Glucose; D011188:Potassium; D002118:Calcium