G-protein modulation of ionic currents in cardiac myocytes
<p>The modulation of L-type calcium current (ICa) and the catecholamine-induced chloride current (ICl,cAMP) by G-protein coupled regulatory pathways were studied in isolated guinea pig cardiac ventricular myocytes using the whole cell patch clamp and flash photolysis techniques. A number of no...
| Main Authors: | , |
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
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2000
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| Subjects: |
| _version_ | 1797083176015757312 |
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| author | Goodstadt, L Leo Goodstadt |
| author2 | Powell, T |
| author_facet | Powell, T Goodstadt, L Leo Goodstadt |
| author_sort | Goodstadt, L |
| collection | OXFORD |
| description | <p>The modulation of L-type calcium current (ICa) and the catecholamine-induced chloride current (ICl,cAMP) by G-protein coupled regulatory pathways were studied in isolated guinea pig cardiac ventricular myocytes using the whole cell patch clamp and flash photolysis techniques. A number of novel findings are reported in this thesis.</p> <p>The rapid release of GTP, the natural ligand of G-proteins, from its inert caged precursor produced a large enhancement of ICa which could be detected within 20 ms of the photolysing light pulse. A fast component of this response persisted under conditions of current rundown and inhibition of cAMP-dependent phosphorylation. This suggests the involvement of a membrane-delimited pathway not dependent on soluble second messengers. The photorelease of the non-hydrolysable GTPγS caused a biphasic increase in ICa in the majority of myocytes and a sustained response in the others.</p> <p>Pipette dialysis with GTPγS had a three-fold effect: pertussis toxin-sensitive inhibition of the ICa responses to isoprenaline, forskolin and photoreleased GTP; competitive inhibition of the enhancement of ICa by further photoreleased GTPγS; and modulation of the kinetics of cAMP-dependent activation of ICl,cAMP and ICa without any significant changes in their magnitudes.</p> <p>The flash photolysis of caged cAMP produced large increases in both ICl,cAMP and ICa but the latter was more than twice as sensitive to cAMP (EC50 = ~ 1.1 μM and ~ 0.47 μM).</p> <p>Urotensin has recently been identified as the ligand for a previously orphaned G-protein coupled receptor, and has been shown to be a potent chronic vasoconstrictor. This thesis reports an additional modulatory effect on ICl,cAMP. μM urotensin had no effect on its own but potentiated responses to sub-maximal sympathetic stimulation.</p> <p>Estrogen reduces forskolin- and isoprenaline-stimulated cAMP accumulation in the rat heart and inhibits cardiac ICa via a G-protein. However, the application of μM ß-estradiol to guinea pig myocytes in the presence of low doses of either forskolin (0.5 μM) or isoprenaline (20 nM) produced large increases in ICl,cAMP. This effect was mediated by a cell surface receptor. The involvement of nitric oxide synthase (NOS) was not required, unlike in acute estrogenic responses in vascular endothelia. Raloxifene, a selective estrogen receptor modulator (SERM), was similarly able to potentiate the results of sympathetic stimulation but with a much slower time course.</p> |
| first_indexed | 2024-03-07T01:38:02Z |
| format | Thesis |
| id | oxford-uuid:95df1add-328f-4045-a357-5e5875502812 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T01:38:02Z |
| publishDate | 2000 |
| record_format | dspace |
| spelling | oxford-uuid:95df1add-328f-4045-a357-5e58755028122022-03-26T23:49:15ZG-protein modulation of ionic currents in cardiac myocytesThesishttp://purl.org/coar/resource_type/c_db06uuid:95df1add-328f-4045-a357-5e5875502812PhysiologyEnglishOxford University Research Archive - Valet2000Goodstadt, LLeo GoodstadtPowell, T<p>The modulation of L-type calcium current (ICa) and the catecholamine-induced chloride current (ICl,cAMP) by G-protein coupled regulatory pathways were studied in isolated guinea pig cardiac ventricular myocytes using the whole cell patch clamp and flash photolysis techniques. A number of novel findings are reported in this thesis.</p> <p>The rapid release of GTP, the natural ligand of G-proteins, from its inert caged precursor produced a large enhancement of ICa which could be detected within 20 ms of the photolysing light pulse. A fast component of this response persisted under conditions of current rundown and inhibition of cAMP-dependent phosphorylation. This suggests the involvement of a membrane-delimited pathway not dependent on soluble second messengers. The photorelease of the non-hydrolysable GTPγS caused a biphasic increase in ICa in the majority of myocytes and a sustained response in the others.</p> <p>Pipette dialysis with GTPγS had a three-fold effect: pertussis toxin-sensitive inhibition of the ICa responses to isoprenaline, forskolin and photoreleased GTP; competitive inhibition of the enhancement of ICa by further photoreleased GTPγS; and modulation of the kinetics of cAMP-dependent activation of ICl,cAMP and ICa without any significant changes in their magnitudes.</p> <p>The flash photolysis of caged cAMP produced large increases in both ICl,cAMP and ICa but the latter was more than twice as sensitive to cAMP (EC50 = ~ 1.1 μM and ~ 0.47 μM).</p> <p>Urotensin has recently been identified as the ligand for a previously orphaned G-protein coupled receptor, and has been shown to be a potent chronic vasoconstrictor. This thesis reports an additional modulatory effect on ICl,cAMP. μM urotensin had no effect on its own but potentiated responses to sub-maximal sympathetic stimulation.</p> <p>Estrogen reduces forskolin- and isoprenaline-stimulated cAMP accumulation in the rat heart and inhibits cardiac ICa via a G-protein. However, the application of μM ß-estradiol to guinea pig myocytes in the presence of low doses of either forskolin (0.5 μM) or isoprenaline (20 nM) produced large increases in ICl,cAMP. This effect was mediated by a cell surface receptor. The involvement of nitric oxide synthase (NOS) was not required, unlike in acute estrogenic responses in vascular endothelia. Raloxifene, a selective estrogen receptor modulator (SERM), was similarly able to potentiate the results of sympathetic stimulation but with a much slower time course.</p> |
| spellingShingle | Physiology Goodstadt, L Leo Goodstadt G-protein modulation of ionic currents in cardiac myocytes |
| title | G-protein modulation of ionic currents in cardiac myocytes |
| title_full | G-protein modulation of ionic currents in cardiac myocytes |
| title_fullStr | G-protein modulation of ionic currents in cardiac myocytes |
| title_full_unstemmed | G-protein modulation of ionic currents in cardiac myocytes |
| title_short | G-protein modulation of ionic currents in cardiac myocytes |
| title_sort | g protein modulation of ionic currents in cardiac myocytes |
| topic | Physiology |
| work_keys_str_mv | AT goodstadtl gproteinmodulationofioniccurrentsincardiacmyocytes AT leogoodstadt gproteinmodulationofioniccurrentsincardiacmyocytes |