Inhibition of luteinizing-hormone exocytosis by guanosine 5'-[gamma-thio]triphosphate reveals involvement of a GTP-binding protein distal to second-messenger generation.
Dual inhibitory and stimulatory actions of guanine nucleotides on luteinizing-hormone (LH) exocytosis were observed in primary sheep gonadotropes permeabilized with staphylococcal alpha-toxin. At resting cytosolic [Ca2+]free (pCa 7), 5'-[gamma-thio]triphosphate (GTP[S]) and guanosine 5'-[b...
| Main Authors: | , , , |
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| Format: | Journal article |
| Language: | English |
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1991
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| _version_ | 1826274076424929280 |
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| author | Van Der Merwe, P Millar, R Wakefield, I Davidson, J |
| author_facet | Van Der Merwe, P Millar, R Wakefield, I Davidson, J |
| author_sort | Van Der Merwe, P |
| collection | OXFORD |
| description | Dual inhibitory and stimulatory actions of guanine nucleotides on luteinizing-hormone (LH) exocytosis were observed in primary sheep gonadotropes permeabilized with staphylococcal alpha-toxin. At resting cytosolic [Ca2+]free (pCa 7), 5'-[gamma-thio]triphosphate (GTP[S]) and guanosine 5'-[beta gamma-imido]triphosphate (p[NH]ppG) stimulated rapid LH exocytosis, which was maximal between 5 and 10 min. GTP[S] and p[NH]ppG had similar potencies (50% of maximum effect at 20-50 microM), but the effect of p[NH]ppG was more prolonged. Experiments carried out in the presence of saturating concentrations of phorbol 12-myristate 13-acetate (PMA), or in PMA-desensitized cells, suggested that stimulation by p[NH]ppG is mediated by a mechanism additional to protein kinase C (PKC) activation. Furthermore, p[NH]ppG stimulated LH exocytosis in the presence of saturating cyclic AMP (cAMP) concentrations, although its effect was less than additive. However, when both PMA and cAMP were present, p[NH]ppG did not stimulate a further increase in the rate of LH exocytosis. In contrast, pretreatment of cells with GTP[S] at low [Ca2+]free markedly inhibited subsequent responses to Ca2+, cAMP, PMA, and cAMP plus PMA. This inhibitory effect required lower GTP[S] concentrations than the stimulatory effect (50% inhibition at 1-10 microM), and was not observed with p[NH]ppG. A similar inhibition was observed with adenosine 5'-[gamma-thio]triphosphate, probably by its conversion into GTP[S]. These results suggest that the stimulatory actions of guanine nucleotides can be accounted for by the combined activation of PKC and generation of cAMP, resulting from activation of conventional signal-transducing GTP-binding proteins. The inhibitory effect of GTP[S] can be clearly distinguished and indicates the involvement of a distinct GTP-binding protein in exocytosis at a site distal to second-messenger generation. |
| first_indexed | 2024-03-06T22:37:57Z |
| format | Journal article |
| id | oxford-uuid:5a90cd4f-72af-45c7-b733-c568dc50d0e7 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T22:37:57Z |
| publishDate | 1991 |
| record_format | dspace |
| spelling | oxford-uuid:5a90cd4f-72af-45c7-b733-c568dc50d0e72022-03-26T17:16:29ZInhibition of luteinizing-hormone exocytosis by guanosine 5'-[gamma-thio]triphosphate reveals involvement of a GTP-binding protein distal to second-messenger generation.Journal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:5a90cd4f-72af-45c7-b733-c568dc50d0e7EnglishSymplectic Elements at Oxford1991Van Der Merwe, PMillar, RWakefield, IDavidson, JDual inhibitory and stimulatory actions of guanine nucleotides on luteinizing-hormone (LH) exocytosis were observed in primary sheep gonadotropes permeabilized with staphylococcal alpha-toxin. At resting cytosolic [Ca2+]free (pCa 7), 5'-[gamma-thio]triphosphate (GTP[S]) and guanosine 5'-[beta gamma-imido]triphosphate (p[NH]ppG) stimulated rapid LH exocytosis, which was maximal between 5 and 10 min. GTP[S] and p[NH]ppG had similar potencies (50% of maximum effect at 20-50 microM), but the effect of p[NH]ppG was more prolonged. Experiments carried out in the presence of saturating concentrations of phorbol 12-myristate 13-acetate (PMA), or in PMA-desensitized cells, suggested that stimulation by p[NH]ppG is mediated by a mechanism additional to protein kinase C (PKC) activation. Furthermore, p[NH]ppG stimulated LH exocytosis in the presence of saturating cyclic AMP (cAMP) concentrations, although its effect was less than additive. However, when both PMA and cAMP were present, p[NH]ppG did not stimulate a further increase in the rate of LH exocytosis. In contrast, pretreatment of cells with GTP[S] at low [Ca2+]free markedly inhibited subsequent responses to Ca2+, cAMP, PMA, and cAMP plus PMA. This inhibitory effect required lower GTP[S] concentrations than the stimulatory effect (50% inhibition at 1-10 microM), and was not observed with p[NH]ppG. A similar inhibition was observed with adenosine 5'-[gamma-thio]triphosphate, probably by its conversion into GTP[S]. These results suggest that the stimulatory actions of guanine nucleotides can be accounted for by the combined activation of PKC and generation of cAMP, resulting from activation of conventional signal-transducing GTP-binding proteins. The inhibitory effect of GTP[S] can be clearly distinguished and indicates the involvement of a distinct GTP-binding protein in exocytosis at a site distal to second-messenger generation. |
| spellingShingle | Van Der Merwe, P Millar, R Wakefield, I Davidson, J Inhibition of luteinizing-hormone exocytosis by guanosine 5'-[gamma-thio]triphosphate reveals involvement of a GTP-binding protein distal to second-messenger generation. |
| title | Inhibition of luteinizing-hormone exocytosis by guanosine 5'-[gamma-thio]triphosphate reveals involvement of a GTP-binding protein distal to second-messenger generation. |
| title_full | Inhibition of luteinizing-hormone exocytosis by guanosine 5'-[gamma-thio]triphosphate reveals involvement of a GTP-binding protein distal to second-messenger generation. |
| title_fullStr | Inhibition of luteinizing-hormone exocytosis by guanosine 5'-[gamma-thio]triphosphate reveals involvement of a GTP-binding protein distal to second-messenger generation. |
| title_full_unstemmed | Inhibition of luteinizing-hormone exocytosis by guanosine 5'-[gamma-thio]triphosphate reveals involvement of a GTP-binding protein distal to second-messenger generation. |
| title_short | Inhibition of luteinizing-hormone exocytosis by guanosine 5'-[gamma-thio]triphosphate reveals involvement of a GTP-binding protein distal to second-messenger generation. |
| title_sort | inhibition of luteinizing hormone exocytosis by guanosine 5 gamma thio triphosphate reveals involvement of a gtp binding protein distal to second messenger generation |
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