title: Basal and physiological Ca(2+) leak from the endoplasmic reticulum of pancreatic acinar cells. Second messenger-activated channels and translocons.
abstract: We have studied the Ca(2+) leak pathways in the endoplasmic reticulum of pancreatic acinar cells by directly measuring Ca(2+) in the endoplasmic reticulum ([Ca(2+)](ER)). Cytosolic Ca(2+) ([Ca(2+)](C)) was clamped to the resting level by a BAPTA-Ca(2+) mixture. Administration of cholecystokinin within the physiological concentration range caused a graded decrease of [Ca(2+)](ER), and the rate of Ca(2+) release generated by 10 pm cholecystokinin is at least 3x as fast as the basal Ca(2+) leak revealed by inhibition of the endoplasmic reticulum Ca(2+)-ATPase. Acetylcholine also evokes a dose-dependent decrease of [Ca(2+)](ER), with an EC(50) of 0.98 +/- 0.06 microm. Inhibition of receptors for inositol 1,4,5-trisphosphate (IP(3)) by heparin or flunarizine blocks the effect of acetylcholine but only partly blocks the effect of cholecystokinin. 8-NH(2) cyclic ADP-ribose (20 microm) inhibits the action of cholecystokinin, but not of acetylcholine(.) The basal Ca(2+) leak from the endoplasmic reticulum is not blocked by antagonists of the IP(3) receptor, the ryanodine receptor, or the receptor for nicotinic acid adenine dinucleotide phosphate. However, treatment with puromycin (0.1-1 mm) to remove nascent polypeptides from ribosomes increases Ca(2+) leak from the endoplasmic reticulum by a mechanism independent of the endoplasmic reticulum Ca(2+) pumps and of the receptors for IP(3) or ryanodine.
authors: Medical Research Council Secretory Control Research Group, The Physiological Laboratory, University of Liverpool, Liverpool L69 3BX, United Kingdom. rlomax@liv.ac.uk
authors: Richard B
authors: RB
authors: Lomax
authors: Cristina
authors: C
authors: Camello
authors: Fabien
authors: F
authors: Van Coppenolle
authors: Ole H
authors: OH
authors: Petersen
authors: Alexei V
authors: AV
authors: Tepikin
mesh_terms: D000109:Acetylcholine / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002463:Cell Membrane Permeability / Q000187:drug effects; D002766:Cholecystokinin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D005444:Flunarizine / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D007202:Indicators and Reagents; D053496:Inositol 1,4,5-Trisphosphate Receptors; D051379:Mice; D010179:Pancreas / Q000187:drug effects / Q000378:metabolism*; D011485:Protein Binding; D011691:Puromycin / Q000494:pharmacology; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D015290:Second Messenger Systems / Q000502:physiology*
chemical_list: D015220:Calcium Channels; D007202:Indicators and Reagents; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel; D011691:Puromycin; D004533:Egtazic Acid; D006493:Heparin; D002766:Cholecystokinin; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D000109:Acetylcholine; D005444:Flunarizine; D002118:Calcium