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

Berthier C, Kutchukian C, Bouvard C, Okamura Y, Jacquemond V - J. Gen. Physiol. (2015)

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.

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Affiliation: Centre National de la Recherche Scientifique UMR 5534, Université Lyon 1, Centre de Génétique et de Physiologie Moléculaire et Cellulaire, 69100 Villeurbanne, France.

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Ca2+ current after strong depolarizing pulses in Ci-VSP–expressing fibers. In each panel, top traces show the two voltage-pulse protocols that were applied to the fiber; the protocol with prepulse to 120 mV (test) was bracketed by two protocols with prepulse to 20 mV (controls). (A–C) Superimposed membrane current records in response to the above shown protocols. Currents recorded during the two control protocols are in black, whereas current elicited by the test protocol is presented in red. In A, records are presented at both low (top) and high magnification (bottom). In B and C, only the high magnification views are presented. (D) Mean values for the ratio of Ca2+ current amplitude after the prepulse to 120 mV to its amplitude after the prepulse to 20 mV; values are plotted versus the pulse interval between the pre- and test pulses. Results are from seven VSP-negative and eight Ci-VSP–positive fibers. Error bars represent ± SEM.
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fig8: Ca2+ current after strong depolarizing pulses in Ci-VSP–expressing fibers. In each panel, top traces show the two voltage-pulse protocols that were applied to the fiber; the protocol with prepulse to 120 mV (test) was bracketed by two protocols with prepulse to 20 mV (controls). (A–C) Superimposed membrane current records in response to the above shown protocols. Currents recorded during the two control protocols are in black, whereas current elicited by the test protocol is presented in red. In A, records are presented at both low (top) and high magnification (bottom). In B and C, only the high magnification views are presented. (D) Mean values for the ratio of Ca2+ current amplitude after the prepulse to 120 mV to its amplitude after the prepulse to 20 mV; values are plotted versus the pulse interval between the pre- and test pulses. Results are from seven VSP-negative and eight Ci-VSP–positive fibers. Error bars represent ± SEM.

Mentions: The above data are consistent with the possibility that activation of VSP in the transverse tubule membrane affects Ca2+ release. We examined whether the function of Cav1.1, which acts both as voltage sensor for E-C coupling and as voltage-dependent Ca2+ channel, would be affected after VSP activation. For this, we measured the Ca2+ current in fibers challenged by a double-pulse protocol. The membrane voltage was first stepped from −80 to 20 mV for 5 s (prepulse) and then, after a 1-s delay, from −80 to 20 mV for 1 s (test pulse). The double pulse was then applied with the prepulse to 120 mV to activate the VSP and then again with the prepulse to 20 mV as a bracketing control. In each fiber, the whole protocol was repeated with a 2-s and with a 5-s interval between the prepulse and the test pulse. Corresponding membrane current traces from a Ci-VSP–expressing fiber are shown in Fig. 8 (A–C). In each panel, the two membrane current records with the prepulse to 20 mV are in black, and the record with the prepulse to 120 mV is in red.


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

Berthier C, Kutchukian C, Bouvard C, Okamura Y, Jacquemond V - J. Gen. Physiol. (2015)

Ca2+ current after strong depolarizing pulses in Ci-VSP–expressing fibers. In each panel, top traces show the two voltage-pulse protocols that were applied to the fiber; the protocol with prepulse to 120 mV (test) was bracketed by two protocols with prepulse to 20 mV (controls). (A–C) Superimposed membrane current records in response to the above shown protocols. Currents recorded during the two control protocols are in black, whereas current elicited by the test protocol is presented in red. In A, records are presented at both low (top) and high magnification (bottom). In B and C, only the high magnification views are presented. (D) Mean values for the ratio of Ca2+ current amplitude after the prepulse to 120 mV to its amplitude after the prepulse to 20 mV; values are plotted versus the pulse interval between the pre- and test pulses. Results are from seven VSP-negative and eight Ci-VSP–positive fibers. Error bars represent ± SEM.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4380211&req=5

fig8: Ca2+ current after strong depolarizing pulses in Ci-VSP–expressing fibers. In each panel, top traces show the two voltage-pulse protocols that were applied to the fiber; the protocol with prepulse to 120 mV (test) was bracketed by two protocols with prepulse to 20 mV (controls). (A–C) Superimposed membrane current records in response to the above shown protocols. Currents recorded during the two control protocols are in black, whereas current elicited by the test protocol is presented in red. In A, records are presented at both low (top) and high magnification (bottom). In B and C, only the high magnification views are presented. (D) Mean values for the ratio of Ca2+ current amplitude after the prepulse to 120 mV to its amplitude after the prepulse to 20 mV; values are plotted versus the pulse interval between the pre- and test pulses. Results are from seven VSP-negative and eight Ci-VSP–positive fibers. Error bars represent ± SEM.
Mentions: The above data are consistent with the possibility that activation of VSP in the transverse tubule membrane affects Ca2+ release. We examined whether the function of Cav1.1, which acts both as voltage sensor for E-C coupling and as voltage-dependent Ca2+ channel, would be affected after VSP activation. For this, we measured the Ca2+ current in fibers challenged by a double-pulse protocol. The membrane voltage was first stepped from −80 to 20 mV for 5 s (prepulse) and then, after a 1-s delay, from −80 to 20 mV for 1 s (test pulse). The double pulse was then applied with the prepulse to 120 mV to activate the VSP and then again with the prepulse to 20 mV as a bracketing control. In each fiber, the whole protocol was repeated with a 2-s and with a 5-s interval between the prepulse and the test pulse. Corresponding membrane current traces from a Ci-VSP–expressing fiber are shown in Fig. 8 (A–C). In each panel, the two membrane current records with the prepulse to 20 mV are in black, and the record with the prepulse to 120 mV is in red.

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.

View Article: PubMed Central - HTML - PubMed

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