title: FKBP12 activates the cardiac ryanodine receptor Ca2+-release channel and is antagonised by FKBP12.6.
abstract: Changes in FKBP12.6 binding to cardiac ryanodine receptors (RyR2) are implicated in mediating disturbances in Ca(2+)-homeostasis in heart failure but there is controversy over the functional effects of FKBP12.6 on RyR2 channel gating. We have therefore investigated the effects of FKBP12.6 and another structurally similar molecule, FKBP12, which is far more abundant in heart, on the gating of single sheep RyR2 channels incorporated into planar phospholipid bilayers and on spontaneous waves of Ca(2+)-induced Ca(2+)-release in rat isolated permeabilised cardiac cells. We demonstrate that FKBP12 is a high affinity activator of RyR2, sensitising the channel to cytosolic Ca(2+), whereas FKBP12.6 has very low efficacy, but can antagonise the effects of FKBP12. Mathematical modelling of the data shows the importance of the relative concentrations of FKBP12 and FKBP12.6 in determining RyR2 activity. Consistent with the single-channel results, physiological concentrations of FKBP12 (3 µM) increased Ca(2+)-wave frequency and decreased the SR Ca(2+)-content in cardiac cells. FKBP12.6, itself, had no effect on wave frequency but antagonised the effects of FKBP12.We provide a biophysical analysis of the mechanisms by which FK-binding proteins can regulate RyR2 single-channel gating. Our data indicate that FKBP12, in addition to FKBP12.6, may be important in regulating RyR2 function in the heart. In heart failure, it is possible that an alteration in the dual regulation of RyR2 by FKBP12 and FKBP12.6 may occur. This could contribute towards a higher RyR2 open probability, 'leaky' RyR2 channels and Ca(2+)-dependent arrhythmias.
authors.affiliation: School of Physiology & Pharmacology, Centre for Nanoscience and Quantum Information, and Bristol Heart Institute, University of Bristol, Bristol, United Kingdom.
authors.forename: Elena
authors.initials: E
authors.lastname: Galfré
authors.forename: Samantha J
authors.initials: SJ
authors.lastname: Pitt
authors.forename: Elisa
authors.initials: E
authors.lastname: Venturi
authors.forename: Mano
authors.initials: M
authors.lastname: Sitsapesan
authors.forename: Nathan R
authors.initials: NR
authors.lastname: Zaccai
authors.forename: Krasimira
authors.initials: K
authors.lastname: Tsaneva-Atanasova
authors.forename: Stephen
authors.initials: S
authors.lastname: O'Neill
authors.forename: Rebecca
authors.initials: R
authors.lastname: Sitsapesan
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D015640:Ion Channel Gating / Q000187:drug effects; D008051:Lipid Bilayers / Q000378:metabolism; D008297:Male; D008954:Models, Biological; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D012756:Sheep; D022061:Tacrolimus Binding Protein 1A / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D022021:Tacrolimus Binding Proteins / Q000378:metabolism*; D013997:Time Factors
chemical_list: D008051:Lipid Bilayers; D010743:Phospholipids; D019837:Ryanodine Receptor Calcium Release Channel; D022061:Tacrolimus Binding Protein 1A; D022021:Tacrolimus Binding Proteins; C403484:tacrolimus binding protein 1B; D002118:Calcium