title: Differential effects of maurocalcine on Ca2+ release events and depolarization-induced Ca2+ release in rat skeletal muscle.
abstract: Maurocalcine (MCa), a 33 amino acid toxin obtained from scorpion venom, has been shown to interact with the isolated skeletal-type ryanodine receptor (RyR1) and to strongly modify its calcium channel gating. In this study, we explored the effects of MCa on RyR1 in situ to establish whether the functional interaction of RyR1 with the voltage-sensing dihydropyridine receptor (DHPR) would modify the ability of MCa to interact with RyR1. In developing skeletal muscle cells the addition of MCa into the external medium induced a calcium transient resulting from RyR1 activation and strongly inhibited the effect of the RyR1 agonist chloro-m-cresol. In contrast, MCa failed to affect the depolarization-induced Ca(2+) release. In intact adult fibres MCa did not induce any change in the cytosolic Ca(2+) concentration. However, when the surface membrane was permeabilized and calcium release events were readily observable, MCa had a time-dependent dual effect: it first increased event frequency, from 0.060 +/- 0.002 to 0.150 +/- 0.007 sarcomere(-1) s(-1), and reduced the amplitude of individual events without modifying their spatial distribution. Later on it induced the appearance of long-lasting events resembling the embers observed in control conditions but having a substantially longer duration. We propose that the functional coupling of DHPRs and RyR1s within a Ca(2+) release unit prevents MCa from either reaching its binding site or from being able to modify the gating not only of the RyR1s physically coupled to DHPRs but all RyR1s within the Ca(2+) release unit.
authors.affiliation: Department of Physiology, RCMM, MHCS, University of Debrecen, Hungary.
authors.forename: Henrietta
authors.initials: H
authors.lastname: Szappanos
authors.forename: Sophia
authors.initials: S
authors.lastname: Smida-Rezgui
authors.forename: Julianna
authors.initials: J
authors.lastname: Cseri
authors.forename: Cecilia
authors.initials: C
authors.lastname: Simut
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Sabatier
authors.forename: Michel
authors.initials: M
authors.lastname: De Waard
authors.forename: László
authors.initials: L
authors.lastname: Kovács
authors.forename: László
authors.initials: L
authors.lastname: Csernoch
authors.forename: Michel
authors.initials: M
authors.lastname: Ronjat
mesh_terms: D000367:Age Factors; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology; D005260:Female; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology*; D051381:Rats; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology; D012604:Scorpion Venoms / Q000494:pharmacology*
chemical_list: D020746:Calcium Channels, L-Type; D019837:Ryanodine Receptor Calcium Release Channel; D012604:Scorpion Venoms; C406406:maurocalcine; D002118:Calcium