title: Tacrolimus (FK506) modulates calcium release and contractility of intestinal smooth muscle.
abstract: Several proteins have been identified that associate with calcium release channels and potentially regulate their function. Using tacrolimus as a pharmacological tool, we investigated whether the immunophilin FKBP12 modulates ryanodine receptor channels in intestinal smooth muscle. Results with PCR demonstrated the presence of type-3 ryanodine receptor and FKBP12 in this tissue. Tacrolimus caused an irreversible increase of the intracellular calcium concentration, which was abolished by pretreatment with caffeine. The calcium channel blocker verapamil did not affect the response to tacrolimus. Tacrolimus decreased the calcium concentration in the sarcoplasmic reticulum. Caffeine, but not inositol 1,4,5-trisphosphate or heparin, abolished this effect. Finally, tacrolimus significantly and irreversibly decreased the tension generated by intestinal muscle strips. These data support our hypothesis that the immunophilin FKBP12 modulates ryanodine receptor function in smooth muscle. Interactions between such regulatory proteins and calcium release channels may play an important role in excitation-contraction coupling and other intracellular signaling processes.
authors.affiliation: Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242, USA. Klaus-Bielefeldt@mail.int-med.uiowa.edu
authors.forename: K
authors.initials: K
authors.lastname: Bielefeldt
authors.forename: R V
authors.initials: RV
authors.lastname: Sharma
authors.forename: C
authors.initials: C
authors.lastname: Whiteis
authors.forename: E
authors.initials: E
authors.lastname: Yedidag
authors.forename: F M
authors.initials: FM
authors.lastname: Abboud
mesh_terms: D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004247:DNA; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D007422:Intestines; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D016133:Polymerase Chain Reaction; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism; D016559:Tacrolimus / Q000494:pharmacology*; D022021:Tacrolimus Binding Proteins
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D006360:Heat-Shock Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D004247:DNA; D022021:Tacrolimus Binding Proteins; D002118:Calcium; D016559:Tacrolimus