title: The random-coil 'C' fragment of the dihydropyridine receptor II-III loop can activate or inhibit native skeletal ryanodine receptors.
abstract: The actions of peptide C, corresponding to (724)Glu-Pro(760) of the II-III loop of the skeletal dihydropyridine receptor, on ryanodine receptor (RyR) channels incorporated into lipid bilayers with the native sarcoplasmic reticulum membrane show that the peptide is a high-affinity activator of native skeletal RyRs at cytoplasmic concentrations of 100 nM-10 microM. In addition, we found that peptide C inhibits RyRs in a voltage-independent manner when added for longer times or at higher concentrations (up to 150 microM). Peptide C had a random-coil structure indicating that it briefly assumes a variety of structures, some of which might activate and others which might inhibit RyRs. The results suggest that RyR activation and inhibition by peptide C arise from independent stochastic processes. A rate constant of 7.5 x 10(5) s(-1).M(-1) was obtained for activation and a lower estimate for the rate constant for inhibition of 5.9 x 10(3) s(-1).M(-1). The combined actions of peptide C and peptide A (II-III loop sequence (671)Thr-Leu(690)) showed that peptide C prevented activation but not blockage of RyRs by peptide A. We suggest that the effects of peptide C indicate functional interactions between a part of the dihydropyridine receptor and the RyR. These interactions could reflect either dynamic changes that occur during excitation-contraction coupling or interactions between the proteins at rest.
authors.affiliation: Muscle Research Group, John Curtin School of Medical Research, Australian National University, P.O. Box 334, Canberra, ACT 2601, Australia.
authors.forename: Claudia S
authors.initials: CS
authors.lastname: Haarmann
authors.forename: Daniel
authors.initials: D
authors.lastname: Green
authors.forename: Marco G
authors.initials: MG
authors.lastname: Casarotto
authors.forename: Derek R
authors.initials: DR
authors.lastname: Laver
authors.forename: Angela F
authors.initials: AF
authors.lastname: Dulhunty
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D002942:Circular Dichroism; D008051:Lipid Bilayers / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008564:Membrane Potentials / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology*; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000502:physiology
chemical_list: D020746:Calcium Channels, L-Type; D008051:Lipid Bilayers; D010455:Peptides; D019837:Ryanodine Receptor Calcium Release Channel; C050632:polypeptide C; D000255:Adenosine Triphosphate