Desensitization of glucagon-like peptide 1 receptors in insulin-secreting beta TC3 cells: role of PKA-independent mechanisms.
1. The cellular processes involved in the desensitization of the glucagon-like peptide 1 receptors were investigated by measurements of the glucagon-like peptide 1(7-36)amide (GLP-1(7-36)amide)-induced increases in intracellular free Ca2+ concentration ([Ca2+]i) in insulin-secreting beta TC3 cells....
| Main Authors: | , , |
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| 格式: | Journal article |
| 语言: | English |
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1996
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| _version_ | 1826268844645154816 |
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| author | Gromada, J Dissing, S Rorsman, P |
| author_facet | Gromada, J Dissing, S Rorsman, P |
| author_sort | Gromada, J |
| collection | OXFORD |
| description | 1. The cellular processes involved in the desensitization of the glucagon-like peptide 1 receptors were investigated by measurements of the glucagon-like peptide 1(7-36)amide (GLP-1(7-36)amide)-induced increases in intracellular free Ca2+ concentration ([Ca2+]i) in insulin-secreting beta TC3 cells. 2. In the presence of 11.2 mM glucose, stimulation with GLP-1(7-36)amide led to a small membrane depolarization (< 10 mV), induction of electrical activity and a rapid increase in [Ca2+]i. The increase in [Ca2+]i was not observed in the presence of the L-type Ca(2+)-channel antagonist nifedipine. However, nifedipine was ineffective when applied after addition of GLP-1(7-36)amide. 3. The increase in [Ca2+]i evoked by GLP-1-(7-36)amide was transient and even in the continued presence of the agonist, [Ca2+]i returned to the basal value within 4-5 min. The latter process was slowed, but not prevented, by inhibition of protein kinase C (PKC) by staurosporine and Ro31-8220. 4. Short pretreatment of the cells with the phorbol ester, 4-beta-phorbol-12-beta-myristate-13-alpha-acetate (PMA), an activator of PKC, reduced the GLP-1(7-36)amide-evoked increase in [Ca2+]i by 75%. This effect of PMA was fully reversed by staurosporine and Ro31-8220. 5. The ability of GLP-1(7-36)amide to increase [Ca2+]i disappeared upon pre-exposure of the cells to the hormone (desensitization). This process was maximal within 5 min of exposure to the agonist. Following removal of the agonist from the medium, the ability to respond to subsequent stimulation by GLP-1(7-36)amide recovered gradually with time; half and complete recovery requiring > 20 min and 60 min, respectively. The desensitizing action of GLP-1(7-36)amide persisted in the presence of either staurosporine or forskolin and did not require an elevation of [Ca2+]i. 6. Our data suggest that the GLP-1(7-36)amide-evoked increase in [Ca2+]i is initiated by Ca(2+)-influx though voltage-dependent and nifedipine-sensitive L-type Ca2+ channels but depends principally on Ca2+ mobilization from internal stores for its maintenance. The desensitization of the GLP-1 receptors that occurs in the continued presence of the agonist does not result from the activation of protein kinase A or Ca(2+)-dependent kinases/phosphatases. Our data indicate that activation of PKC may contribute to the desensitization of the GLP-1 receptors but that other (PKC-independent) mechanisms also participate in this process. |
| first_indexed | 2024-03-06T21:15:49Z |
| format | Journal article |
| id | oxford-uuid:3fc2e675-54fc-4640-beab-62410d2b791c |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T21:15:49Z |
| publishDate | 1996 |
| record_format | dspace |
| spelling | oxford-uuid:3fc2e675-54fc-4640-beab-62410d2b791c2022-03-26T14:34:00ZDesensitization of glucagon-like peptide 1 receptors in insulin-secreting beta TC3 cells: role of PKA-independent mechanisms.Journal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:3fc2e675-54fc-4640-beab-62410d2b791cEnglishSymplectic Elements at Oxford1996Gromada, JDissing, SRorsman, P1. The cellular processes involved in the desensitization of the glucagon-like peptide 1 receptors were investigated by measurements of the glucagon-like peptide 1(7-36)amide (GLP-1(7-36)amide)-induced increases in intracellular free Ca2+ concentration ([Ca2+]i) in insulin-secreting beta TC3 cells. 2. In the presence of 11.2 mM glucose, stimulation with GLP-1(7-36)amide led to a small membrane depolarization (< 10 mV), induction of electrical activity and a rapid increase in [Ca2+]i. The increase in [Ca2+]i was not observed in the presence of the L-type Ca(2+)-channel antagonist nifedipine. However, nifedipine was ineffective when applied after addition of GLP-1(7-36)amide. 3. The increase in [Ca2+]i evoked by GLP-1-(7-36)amide was transient and even in the continued presence of the agonist, [Ca2+]i returned to the basal value within 4-5 min. The latter process was slowed, but not prevented, by inhibition of protein kinase C (PKC) by staurosporine and Ro31-8220. 4. Short pretreatment of the cells with the phorbol ester, 4-beta-phorbol-12-beta-myristate-13-alpha-acetate (PMA), an activator of PKC, reduced the GLP-1(7-36)amide-evoked increase in [Ca2+]i by 75%. This effect of PMA was fully reversed by staurosporine and Ro31-8220. 5. The ability of GLP-1(7-36)amide to increase [Ca2+]i disappeared upon pre-exposure of the cells to the hormone (desensitization). This process was maximal within 5 min of exposure to the agonist. Following removal of the agonist from the medium, the ability to respond to subsequent stimulation by GLP-1(7-36)amide recovered gradually with time; half and complete recovery requiring > 20 min and 60 min, respectively. The desensitizing action of GLP-1(7-36)amide persisted in the presence of either staurosporine or forskolin and did not require an elevation of [Ca2+]i. 6. Our data suggest that the GLP-1(7-36)amide-evoked increase in [Ca2+]i is initiated by Ca(2+)-influx though voltage-dependent and nifedipine-sensitive L-type Ca2+ channels but depends principally on Ca2+ mobilization from internal stores for its maintenance. The desensitization of the GLP-1 receptors that occurs in the continued presence of the agonist does not result from the activation of protein kinase A or Ca(2+)-dependent kinases/phosphatases. Our data indicate that activation of PKC may contribute to the desensitization of the GLP-1 receptors but that other (PKC-independent) mechanisms also participate in this process. |
| spellingShingle | Gromada, J Dissing, S Rorsman, P Desensitization of glucagon-like peptide 1 receptors in insulin-secreting beta TC3 cells: role of PKA-independent mechanisms. |
| title | Desensitization of glucagon-like peptide 1 receptors in insulin-secreting beta TC3 cells: role of PKA-independent mechanisms. |
| title_full | Desensitization of glucagon-like peptide 1 receptors in insulin-secreting beta TC3 cells: role of PKA-independent mechanisms. |
| title_fullStr | Desensitization of glucagon-like peptide 1 receptors in insulin-secreting beta TC3 cells: role of PKA-independent mechanisms. |
| title_full_unstemmed | Desensitization of glucagon-like peptide 1 receptors in insulin-secreting beta TC3 cells: role of PKA-independent mechanisms. |
| title_short | Desensitization of glucagon-like peptide 1 receptors in insulin-secreting beta TC3 cells: role of PKA-independent mechanisms. |
| title_sort | desensitization of glucagon like peptide 1 receptors in insulin secreting beta tc3 cells role of pka independent mechanisms |
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