Acyl-CoA esters modulate intracellular Ca2+ handling by permeabilized clonal pancreatic beta-cells.
Cytosolic free Ca2+ rises in pancreatic beta-cells in response to glucose stimulation and is part of the coupling to insulin secretion. This study evaluates a possible role for cytosolic long chain acyl-CoA esters in modulating Ca2+ handling by clonal beta-cells (HIT). Intact cells incubated with 20 microM free palmitic acid exhibited a 40% decrease in basal cytosolic free Ca2+. In contrast, acyl-CoA esters, up to a chain length of 16, but not the corresponding fatty acids, significantly lowered the Ca2+ set point maintained by cells permeabilized with saponin. The maximum response to the various acyl-CoA esters increased with increasing chain length, with no differences in the half-maximally effective concentration of 0.5 microM. Long chain acyl-CoA esters caused a 40-50% increase in 45Ca2+ influx into a non-mitochondrial pool in the permeabilized HIT cells, consistent with a stimulatory effect on the endoplasmic reticulum Ca(2+)-ATPase activity, but did not affect inositol 1,4,5-trisphosphate-induced Ca(2+)-efflux. Thapsigargin, an inhibitor of endoplasmic reticulum Ca(2+)-ATPase activity, blocked the decrease in the Ca2+ set point caused by acyl-CoA esters. The ability of acyl-CoA esters to lower the Ca2+ set point depended on the ATP/ADP ratio (or free ADP); the Ca2+ set point was lowered by 36 +/- 3.6% at an ATP/ADP ratio of 90 and by 14 +/- 1.9% at an ATP/ADP ratio of 7. Depletion of cellular protein kinase C did not prevent the acyl-CoA-induced lowering of the Ca2+ set point. These findings suggest that the increases in long chain acyl-CoA esters may play a role in restoring cytosolic free Ca2+ through activation of Ca(2+)-ATPases.
Deeney
J T
JT
Evans Department of Medicine, Boston University School of Medicine, Massachusetts 02118.
Tornheim
K
K
Korchak
H M
HM
Prentki
M
M
Corkey
B E
BE
D000214:Acyl Coenzyme A / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002413:Cations, Divalent; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000201:enzymology; D004952:Esters / Q000378:metabolism; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D007515:Islets of Langerhans / Q000378:metabolism*; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D000214:Acyl Coenzyme A; D002413:Cations, Divalent; D004952:Esters; D005230:Fatty Acids, Nonesterified; D013729:Terpenes; D000244:Adenosine Diphosphate; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium