Defective glucose-dependent endoplasmic reticulum Ca2+ sequestration in diabetic mouse islets of Langerhans.
Non-insulin-dependent diabetes mellitus (NIDDM) is a metabolic disease associated with abnormal insulin secretion, the underlying mechanisms of which are unknown. Glucose-dependent signal transduction pathways were investigated in pancreatic islets derived from the db/db mouse, an animal model of NIDDM. After stimulation with glucose (4-12 mM), the changes in intracellular Ca2+ concentration ([Ca2+]i) were different; unlike control islets, db/db islets lacked an initial reduction of [Ca2+]i and the subsequent [Ca2+]i oscillations following stimulation with 12 mM glucose. The severity of these defects in Ca2+ signaling correlated with the age-dependent development of hyperglycemia. Similarly defective glucose-induced Ca2+ signaling were reproduced in control islets by pre-exposure to thapsigargin, a selective inhibitor of endoplasmic reticulum (ER) Ca(2+)-ATPase. Estimation of ATPase activities from rates of ATP hydrolysis and by immunoblot hybridization with an antiserum directed against the sarco/endoplasmic reticulum Ca(2+)-ATPase both demonstrated that the ER Ca(2+)-ATPase was almost entirely absent from db/db islets. The effects of inhibition of ER Ca(2+)-ATPase on insulin secretion were also examined; a 4-day exposure of control islets to 1 microM thapsigargin resulted in basal and glucose-stimulated insulin secretion levels similar to those found in db/db islets. These results suggest that aberrant ER Ca2+ sequestration underlies the impaired glucose responses in the db/db mouse and may play a role in defective insulin secretion associated with NIDDM.
Roe
M W
MW
Department of Cell Physiology, Glaxo Research Institute, Research Triangle Park, North Carolina 27709.
Philipson
L H
LH
Frangakis
C J
CJ
Kuznetsov
A
A
Mertz
R J
RJ
Lancaster
M E
ME
Spencer
B
B
Worley
J F
JF
Dukes
I D
ID
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002147:Calmodulin / Q000037:antagonists & inhibitors; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology*; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008815:Mice, Inbred Strains; D008817:Mice, Mutant Strains; D012016:Reference Values; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D002147:Calmodulin; D007093:Imidazoles; D007328:Insulin; D013729:Terpenes; C031938:calmidazolium; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D005947:Glucose; D002118:Calcium