title: Calmodulin activation and inhibition of skeletal muscle Ca2+ release channel (ryanodine receptor).
abstract: The calmodulin-binding properties of the rabbit skeletal muscle Ca2+ release channel (ryanodine receptor) and the channel's regulation by calmodulin were determined at < or = 0.1 microM and micromolar to millimolar Ca2+ concentrations. [125I]Calmodulin and [3H]ryanodine binding to sarcoplasmic reticulum (SR) vesicles and purified Ca2+ release channel preparations indicated that the large (2200 kDa) Ca2+ release channel complex binds with high affinity (KD = 5-25 nM) 16 calmodulins at < or = 0.1 microM Ca2+ and 4 calmodulins at 100 microM Ca2+. Calmodulin-binding affinity to the channel showed a broad maximum at pH 6.8 and was highest at 0.15 M KCl at both < or = 0.1 MicroM and 100 microM Ca2+. Under condition closely related to those during muscle contraction and relaxation, the half-times of calmodulin dissociation and binding were 50 +/- 20 s and 30 +/- 10 min, respectively. SR vesicle-45Ca2+ flux, single-channel, and [3H]ryanodine bind measurements showed that, at < or = 0.2 microM Ca2+, calmodulin activated the Ca2+ release channel severalfold. Ar micromolar to millimolar Ca2+ concentrations, calmodulin inhibited the Ca(2+)-activated channel severalfold. Hill coefficients of approximately 1.3 suggested no or only weak cooperative activation and inhibition of Ca2+ release channel activity by calmodulin. These results suggest a role for calmodulin in modulating SR Ca2+ release in skeletal muscle at both resting and elevated Ca2+ concentrations.
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill 27599, USA.
authors.forename: A
authors.initials: A
authors.lastname: Tripathy
authors.forename: L
authors.initials: L
authors.lastname: Xu
authors.forename: G
authors.initials: G
authors.lastname: Mann
authors.forename: G
authors.initials: G
authors.lastname: Meissner
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002147:Calmodulin / Q000378:metabolism / Q000494:pharmacology*; D002148:Calmodulin-Binding Proteins / Q000502:physiology; D007700:Kinetics; D008081:Liposomes; D008564:Membrane Potentials / Q000187:drug effects; D009124:Muscle Proteins / Q000187:drug effects / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011510:Proteolipids / Q000378:metabolism; D011817:Rabbits; D012433:Ryanodine / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000502:physiology*
chemical_list: D015220:Calcium Channels; D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D008081:Liposomes; D009124:Muscle Proteins; D011510:Proteolipids; D019837:Ryanodine Receptor Calcium Release Channel; C020485:proteoliposomes; D012433:Ryanodine; D002118:Calcium