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.

Effects of K-201 on the calcium pump and calcium release channel of rat skeletal muscle

“…Fibers held in sulfate-based internal solution had stable background fluorescence and showed spontaneous elementary calcium release events (ECRE; Fig. 7a) in accordance with previous observations [14,25,33]. Both sparks and embers were readily observable in the absence and in the presence of K-201.…”

“…Fluo-4 was excited at 488 nm (argon ion laser), and emitted light was collected through a band-pass filter and digitized at 12 bit. Elementary calcium-release events were captured using an automatic computer detection method as described in our previous reports [25,27]. Briefly, the program identified elementary events as regions with fluorescence above a relative threshold, calculated from the noise in the images, and having amplitudes greater than 0.2 ΔF/F 0 units.…”

In cellulo phosphorylation induces pharmacological reprogramming of maurocalcin, a cell-penetrating venom peptide

“…MCa binding onto RyR1 also induces Ca 2+ release from sarcoplasmic reticulum vesicles (8). These effects correlate with the induction by MCa of long-lasting subconductance open transitions of purified RyR1 channels reconstituted in artificial lipid bilayers (7,17,18). This positive allosteric activity of MCa is the consequence of its interaction with a cytoplasmic RyR1 domain that directly controls the gating of this calcium channel (19).…”

Small Efficient Cell-penetrating Peptides Derived from Scorpion Toxin Maurocalcine

“…This loop is predominantly involved in excitation-contraction coupling through direct molecular interactions with RyR1 (6,8). This homology has been a source of inspiration to an understanding of how toxins may interfere with the process of excitation-contraction coupling (4,8,9). Third, and this is the scope of this paper, MCa has been shown to act as a cell-penetrating peptide (CPP) (10).…”