Depression of voltage-activated Ca2+ release in skeletal muscle by activation of a voltage-sensing phosphatase.
Bottom Line: However, in Ci-VSP-expressing fibers challenged by 5-s-long depolarizing pulses, the Ca(2+) level late in the pulse (3 s after initiation) was significantly lower at 120 mV than at 20 mV.Our results indicate that the PtdIns(4,5)P2 level is tightly maintained in the transverse tubule membrane of the muscle fibers, and that VSP-induced depletion of PtdIns(4,5)P2 impairs voltage-activated Ca(2+) release from the SR.Because Ca(2+) release is thought to be independent from InsP3 signaling, the effect likely results from an interaction between PtdIns(4,5)P2 and a protein partner of the E-C coupling machinery.
Affiliation: Centre National de la Recherche Scientifique UMR 5534, Université Lyon 1, Centre de Génétique et de Physiologie Moléculaire et Cellulaire, 69100 Villeurbanne, France.Show MeSH
Related in: MedlinePlus
License 1 - License 2
Mentions: The 200-ms pulse-train control and test protocols described above were also tested in fibers expressing Dr-VSP, a teleost orthologue of VSP, which exhibits a more positive voltage dependence than Ci-VSP. As illustrated in Fig. 7 (B and C), Dr-VSP–expressing fibers responded in a similar manner to Ci-VSP–expressing fibers. However, out of seven fibers tested, two did not respond with any drop at all in the ratio (of peak F/F0 values during the test record to corresponding values in the control record) when the pulses to 100 mV were applied. As a consequence, none of the mean ratio values significantly differed from the corresponding ones in the VSP-negative fibers. Still, when testing the mean values versus the hypothesis of the ratio being 1, values for pulses number 15 and above were significantly depressed. Dr-VSP appeared thus less efficient than Ci-VSP in depressing Ca2+ release, but this was expected because it requires more positive voltage steps to be activated.
Affiliation: Centre National de la Recherche Scientifique UMR 5534, Université Lyon 1, Centre de Génétique et de Physiologie Moléculaire et Cellulaire, 69100 Villeurbanne, France.