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dc.contributor.authorRoche, John Patrick
dc.date2022-08-11T08:08:40.000
dc.date.accessioned2022-08-23T16:03:58Z
dc.date.available2022-08-23T16:03:58Z
dc.date.issued1997-05-01
dc.date.submitted2007-03-28
dc.identifier.urihttp://hdl.handle.net/20.500.14038/31593
dc.descriptionIn the process of seeking author's permission to provide full text.
dc.description.abstractModulation of Ca2+ channels is an important mechanism for regulation of synaptic strength. However, it is clear that some Ca2+ current types are insensitive to inhibitory modulation mediated by heterotrimeric G proteins (G protein inhibition), and among currents which are sensitive to G protein inhibition, there is great variation in the magnitude of Ca2+ current inhibition between cells of different origin. For the experiments in this dissertation, I utilized recently cloned Ca2+ channels to determine the minimal combination of Ca2+ channel subunits which would confer G protein sensitivity to the recombinant channels. In addition, I examined the role Ca2+ channel auxiliary subunits play in regulation of Ca2+ channel sensitivity to inhibitory G proteins, and whether channels which were sensitive to G protein inhibition were regulated equivalently by the auxiliary subunits. Finally, I investigated possible mechanisms by which these auxiliary subunits modulate G protein-mediated inhibition of Ca2+ channels. I found that α1A and α1B Ca2+ currents, when expressed in Xenopus oocytes, were sensitive to modulation by G proteins in the absence of any Ca2+ channel auxiliary subunits, while α1C currents were not modulated under the same conditions. I conclude from this data that Ca2+ channel α1 subunits are differentially sensitive to G protein modulation, and the α1 subunit of the class A and B Ca2+ channels is sufficient for G protein modulation. I also tested the ability of Ca2+ channel auxiliary subunits to modulate the magnitude of G protein-mediated inhibition Ca2+ currents. I found that the Ca2+ channel α2 subunit had no effect on the magnitude of G protein inhibition of α1A and α1B currents. However, the Ca2+ channel β3 subunit eliminated tonic G protein inhibition and sharply reduced the magnitude of muscarinic M2 receptor induced G protein inhibition of both α1A and α1B currents. I found, however, that while the magnitude of α1A and α1B current inhibition was equivalent in the absence of auxiliary subunits, the magnitude of inhibition was greater for the α1B channel after co-expression of the Ca2+ channel β3 subunit. These results indicate that the Ca2+ channel β3 subunit reduces the sensitivity of α1A and α1B Ca2+ channels to voltage-dependent G protein modulation, and does so to a greater extent for α1A channels when compared to α1B Ca2+ channels. I found that M2 receptor induced inhibition of α1B currents was more voltage-dependent after expression of the Ca2+ channel β3 subunit. Additionally, the rate relief of G protein inhibition dramatically increased after co-expression of the Ca2+ channel β3 subunit. I also co-expressed G protein subunits, and determined that inhibition of both α1B and α1Bβ3 currents was mediated by the G protein βγ subunit. Furthermore, the rate of voltage-dependent relief of G protein βγ subunit induced inhibition increased after co-expression of the Ca2+ channel β3 subunit, similar to the increased rate of relief of the M2 receptor induced G protein inhibition. These data, along with data which demonstrates that G protein inhibition results from the binding of the G protein βγ subunit to the Ca2+ channel (De Waard et al., 1997), indicate that the Ca2+ channel β3 subunit subunit reduces the magnitude of G protein inhibition of α1B Ca2+ currents by increasing the rate of dissociation of the G protein βγ subunit, such that moderate depolarizations used to activate the channel also relieve a large portion of the G protein inhibition.
dc.language.isoen_US
dc.rightsCopyright is held by the author, with all rights reserved.
dc.subjectCalcium Channels
dc.subjectGTP-Binding Proteins
dc.subjectSignal Transduction
dc.subjectAcademic Dissertations
dc.subjectLife Sciences
dc.subjectMedicine and Health Sciences
dc.titleThe Role of Ca<sup>2+</sup> Channel Subunit Composition in G Protein-Mediated Inhibition of Ca<sup>2+</sup> Channels: a Disstertation
dc.typeDoctoral Dissertation
dc.identifier.legacycoverpagehttps://escholarship.umassmed.edu/gsbs_diss/281
dc.legacy.embargo2017-04-24T00:00:00-07:00
dc.identifier.contextkey284791
html.description.abstract<p>Modulation of Ca<sup>2+</sup> channels is an important mechanism for regulation of synaptic strength. However, it is clear that some Ca<sup>2+</sup> current types are insensitive to inhibitory modulation mediated by heterotrimeric G proteins (G protein inhibition), and among currents which are sensitive to G protein inhibition, there is great variation in the magnitude of Ca<sup>2+</sup> current inhibition between cells of different origin. For the experiments in this dissertation, I utilized recently cloned Ca<sup>2+</sup> channels to determine the minimal combination of Ca<sup>2+</sup> channel subunits which would confer G protein sensitivity to the recombinant channels. In addition, I examined the role Ca<sup>2+</sup> channel auxiliary subunits play in regulation of Ca<sup>2+</sup> channel sensitivity to inhibitory G proteins, and whether channels which were sensitive to G protein inhibition were regulated equivalently by the auxiliary subunits. Finally, I investigated possible mechanisms by which these auxiliary subunits modulate G protein-mediated inhibition of Ca<sup>2+</sup> channels.</p> <p>I found that α<sub>1A</sub> and α<sub>1B</sub> Ca<sup>2+</sup> currents, when expressed in Xenopus oocytes, were sensitive to modulation by G proteins in the absence of any Ca<sup>2+</sup> channel auxiliary subunits, while α<sub>1C</sub> currents were not modulated under the same conditions. I conclude from this data that Ca<sup>2+</sup> channel α<sub>1</sub> subunits are differentially sensitive to G protein modulation, and the α<sub>1</sub> subunit of the class A and B Ca<sup>2+</sup> channels is sufficient for G protein modulation.</p> <p>I also tested the ability of Ca<sup>2+</sup> channel auxiliary subunits to modulate the magnitude of G protein-mediated inhibition Ca<sup>2+</sup> currents. I found that the Ca<sup>2+</sup> channel α<sub>2</sub> subunit had no effect on the magnitude of G protein inhibition of α<sub>1A</sub> and α<sub>1B</sub> currents. However, the Ca<sup>2+</sup> channel β<sub>3</sub> subunit eliminated tonic G protein inhibition and sharply reduced the magnitude of muscarinic M<sub>2</sub> receptor induced G protein inhibition of both α<sub>1A</sub> and α<sub>1B</sub> currents. I found, however, that while the magnitude of α<sub>1A</sub> and α<sub>1B</sub> current inhibition was equivalent in the absence of auxiliary subunits, the magnitude of inhibition was greater for the α<sub>1B</sub> channel after co-expression of the Ca<sup>2+</sup> channel β<sub>3</sub> subunit. These results indicate that the Ca<sup>2+</sup> channel β<sub>3</sub> subunit reduces the sensitivity of α<sub>1A</sub> and α<sub>1B</sub> Ca<sup>2+</sup> channels to voltage-dependent G protein modulation, and does so to a greater extent for α<sub>1A</sub> channels when compared to α<sub>1B</sub> Ca<sup>2+</sup> channels.</p> <p>I found that M<sub>2</sub> receptor induced inhibition of α<sub>1B</sub> currents was more voltage-dependent after expression of the Ca<sup>2+</sup> channel β<sub>3</sub> subunit. Additionally, the rate relief of G protein inhibition dramatically increased after co-expression of the Ca<sup>2+</sup> channel β<sub>3</sub> subunit. I also co-expressed G protein subunits, and determined that inhibition of both α<sub>1B</sub> and α<sub>1B</sub>β<sub>3</sub> currents was mediated by the G protein βγ subunit. Furthermore, the rate of voltage-dependent relief of G protein βγ subunit induced inhibition increased after co-expression of the Ca<sup>2+</sup> channel β<sub>3</sub> subunit, similar to the increased rate of relief of the M<sub>2</sub> receptor induced G protein inhibition. These data, along with data which demonstrates that G protein inhibition results from the binding of the G protein βγ subunit to the Ca<sup>2+</sup> channel (De Waard et al., 1997), indicate that the Ca<sup>2+</sup> channel β<sub>3</sub> subunit subunit reduces the magnitude of G protein inhibition of α<sub>1B</sub> Ca<sup>2+</sup> currents by increasing the rate of dissociation of the G protein βγ subunit, such that moderate depolarizations used to activate the channel also relieve a large portion of the G protein inhibition.</p>
dc.identifier.submissionpathgsbs_diss/281
dc.contributor.departmentGraduate School of Biomedical Sciences
dc.contributor.departmentDepartment of Pharmacology


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