Triadin (Trisk 95) overexpression blocks excitation-contraction coupling in rat skeletal myotubes.

To identify the function of triadin in skeletal muscle, adenovirus-mediated overexpression of Trisk 95 or Trisk 51, the two major skeletal muscle isoforms, was induced in rat skeletal muscle primary cultures, and the physiological behavior of the modified cells was analyzed. Overexpression did not modify the expression level of their protein partners ryanodine receptor, dihydropyridine receptor, and the other triadin. Caffeine-induced calcium release was also unaffected by triadin overexpression.

Triadins are not triad-specific proteins: two new skeletal muscle triadins possibly involved in the architecture of sarcoplasmic reticulum.

We have cloned two new triadin isoforms from rat skeletal muscle, Trisk 49 and Trisk 32, which were named according to their theoretical molecular masses (49 and 32 kDa, respectively). Specific antibodies directed against each protein were produced to characterize both new triadins. Both are expressed in adult rat skeletal muscle, and their expression in slow twitch muscle is lower than that in fast twitch muscle.

Differential effects of maurocalcine on Ca2+ release events and depolarization-induced Ca2+ release in rat skeletal muscle.

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.

Transduction of the scorpion toxin maurocalcine into cells. Evidence that the toxin crosses the plasma membrane.

Maurocalcine (MCa) is a 33-amino-acid residue peptide toxin isolated from the scorpion Scorpio maurus palmatus. External application of MCa to cultured myotubes is known to produce Ca2+ release from intracellular stores. MCa binds directly to the skeletal muscle isoform of the ryanodine receptor, an intracellular channel target of the endoplasmic reticulum, and induces long lasting channel openings in a mode of smaller conductance.

Junctate is a key element in calcium entry induced by activation of InsP3 receptors and/or calcium store depletion.

In many cell types agonist-receptor activation leads to a rapid and transient release of Ca(2+) from intracellular stores via activation of inositol 1,4,5 trisphosphate (InsP(3)) receptors (InsP(3)Rs). Stimulated cells activate store- or receptor-operated calcium channels localized in the plasma membrane, allowing entry of extracellular calcium into the cytoplasm, and thus replenishment of intracellular calcium stores. Calcium entry must be finely regulated in order to prevent an excessive intracellular calcium increase.

Monolayer versus aggregate balance in survival process for EGF-induced apoptosis in A431 carcinoma cells: Implication of ROS-P38 MAPK-integrin alpha2beta1 pathway.

A431 cells escape EGF-induced apoptosis by forming cell aggregates. We show that these clusters migrate and merge with neighboring ones, resulting in larger structures composed of a multilayer central (3D) population surrounded by a cell monolayer (2D). We found that after 48 hr of 10 nM EGF treatment, 3D structure formation correlates with alpha2beta1 integrin upregulation.

Critical amino acid residues determine the binding affinity and the Ca2+ release efficacy of maurocalcine in skeletal muscle cells.

Maurocalcine (MCa) is a 33 amino acid residue peptide toxin isolated from the scorpion Scorpio maurus palmatus. MCa and mutated analogues were chemically synthesized, and their interaction with the skeletal muscle ryanodine receptor (RyR1) was studied on purified RyR1, sarcoplasmic reticulum (SR) vesicles, and cultured myotubes. MCa strongly potentiates [3H]ryanodine binding on SR vesicles (7-fold at pCa 5) with an apparent EC50 of 12 nm.