AJP - Endocrinology and Metabolism, Vol 247, Issue 6 719-E725, Copyright © 1984 by American Physiological Society
Mobilization of 45Ca from insulin-producing RINm5F cells attached to microcarriers
H. Abrahamsson, P. O. Berggren and B. Hellman
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.
