CA2-SECRETING CELLS - LACK OF EFFECT OF CADP RIBOSE( STORES IN INSULIN)

Ca2+ stores were examined in several insulin secreting cell types by m easuring uptake and release of Ca2+ by permeabilised cells. In pancrea tic islet cells or INS-1 cells, <20% of the ATP-dependent, thapsigargi n-sensitive Ca2+ pool could be released by saturating concentrations o f inositol (1,4,5)P-3 (InsP(3)). InsP(3) released > 60% of the thapsig argin-sensitive Ca2+ pool in RINm5F cells. The total Ca2+ content of t he thapsigargin-sensitive pool was similar in each of these cell types . Neither cADP ribose (cADPR; 1 mu M) nor caffeine (10 mM) caused sign ificant Ca2+ release from any of the permeabilised insulin-secreting c ell preparations. ATP elicited similar increases in intracellular Ca2 concentration ([Ca2+](i)) in single, living INS-1 and RINm5F cells, a nd similar fold increases in InsP(3) levels in cell populations. The C a2+ ATPase inhibitor thapsigargin, added after ATP, caused smaller [Ca 2+](i) increases in RINm5F than in INS-1 cells. This is consistent wit h the presence of a smaller lnsP(3)-sensitive Ca2+ pool in living INS- 1 cells. The data indicate that InsP(3) receptors are present in only a small subfraction of the Ca2+ ATPase-containing Ca2+ stores in INS-1 and pancreatic beta-cells, and that cADP ribose/caffeine-sensitive Ca 2+-induced Ca2+ release channels may be entirely absent from this endo crine cell type.