Depression of voltage-activated Ca2+ release in skeletal muscle by activation of a voltage-sensing phosphatase

作者：Berthier Christine; Kutchukian Candice; Bouvard Clement; Okamura Yasushi; Jacquemond Vincent^*

来源：Journal of General Physiology, 2015, 145(4): 315-330.

DOI：10.1085/jgp.201411309

Phosphoinositides act as signaling molecules in numerous cellular transduction processes, and phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5) P-2) regulates the function of several types of plasma membrane ion channels. We investigated the potential role of PtdIns(4,5) P-2 in Ca2+ homeostasis and excitation-contraction (E-C) coupling of mouse muscle fibers using in vivo expression of the voltage-sensing phosphatases (VSPs) Ciona intestinalis VSP (Ci-VSP) or Danio rerio VSP (Dr-VSP). Confocal images of enhanced green fluorescent protein-tagged Dr-VSP revealed a banded pattern consistent with VSP localization within the transverse tubule membrane. Rhod-2 Ca2+ transients generated by 0.5-s-long voltage-clamp depolarizing pulses sufficient to elicit Ca2+ release from the sarcoplasmic reticulum (SR) but below the range at which VSPs are activated were unaffected by the presence of the VSPs. However, in Ci-VSP-expressing fibers challenged by 5-s-long depolarizing pulses, the Ca2+ level late in the pulse (3 s after initiation) was significantly lower at 120 mV than at 20 mV. Furthermore, Ci-VSP-expressing fibers showed a reversible depression of Ca2+ release during trains, with the peak Ca2+ transient being reduced by similar to 30% after the application of 10 200-ms-long pulses to 100 mV. A similar depression was observed in Dr-VSP-expressing fibers. Cav1.1 Ca2+ channel-mediated current was unaffected by Ci-VSP activation. In fibers expressing Ci-VSP and a pleckstrin homology domain fused with monomeric red fluorescent protein (PLC delta 1PH-mRFP), depolarizing pulses elicited transient changes in mRFP fluorescence consistent with release of transverse tubule-bound PLC delta 1PH domain into the cytosol; the voltage sensitivity of these changes was consistent with that of Ci-VSP activation, and recovery occurred with a time constant in the 10-s range. Our results indicate that the PtdIns(4,5) P-2 level is tightly maintained in the transverse tubule membrane of the muscle fibers, and that VSP-induced depletion of PtdIns(4,5) P-2 impairs voltage-activated Ca2+ release from the SR. Because Ca2+ release is thought to be independent from InsP(3) signaling, the effect likely results from an interaction between PtdIns(4,5) P-2 and a protein partner of the E-C coupling machinery.

• 出版日期2015-4