title: A calcium conducting channel akin to a calcium pump.
abstract: Calcium conducting channels were studied in blebs of sarcoplasmic reticulum described by Stein & Palade (1988). The calcium channels had at least three conductance states (70 pS, 50 pS and 37 pS) and were weakly selective for calcium ions, with a permeability ratio Ca2+ to K+ of about 3.4. The open probability of the channel was strongly voltage dependent, decreasing at positive membrane voltages. 10 microM ryanodine and 5 microM ruthenium red had no effect on this channel; neither did millimolar concentrations of ATP, Mg2+, caffeine, and Ca2+, implying that the calcium conducting channels are not ryanodine receptors. Several calcium pump inhibitors--namely, vanadate, AlF4-, reactive red 120, and cyclopiazonic acid--had obvious effects on the calcium conducting channels, suggesting that the calcium conducting channel of SR membrane blebs is some form of the SR calcium pump.
authors.affiliation: Department of Physiology, Rush Medical College, Chicago, Illinois 60612.
authors.forename: J
authors.initials: J
authors.lastname: Wang
authors.forename: J M
authors.initials: JM
authors.lastname: Tang
authors.forename: R S
authors.initials: RS
authors.lastname: Eisenberg
mesh_terms: D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D007211:Indoles / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D011892:Rana catesbeiana; D012430:Ruthenium Red / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000737:chemistry / Q000648:ultrastructure; D014227:Triazines / Q000494:pharmacology; D014638:Vanadates / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D007211:Indoles; D015221:Potassium Channels; D014227:Triazines; D012430:Ruthenium Red; D012433:Ryanodine; D014638:Vanadates; C042516:reactive red 120 dye; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium; C000543:cyclopiazonic acid