Involvement of Protein Kinase C and Protein Tyrosine Kinase in Thyrotropin-Releasing Hormone-Induced Stimulation ofα -Melanocyte-Stimulating Hormone Secretion in Frog Melanotrope Cells*

Galas, Ludovic; Lamacz, Marek; Garnier, M; Roubos, Eric W.; Tonon, Marie‐Christine; Vaudry, Hubert

doi:10.1210/endo.140.7.6772

Cited by 10 publications

(1 citation statement)

References 49 publications

(38 reference statements)

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“…Frog pituitary melanotropes were cultured as previously described [35]. Briefly, neurointermediate lobes were dissociated by enzymatic and mechanical dispersion.…”

Section: Methodsmentioning

confidence: 99%

Neurotensin Modulates the Electrical Activity of Frog Pituitary Melanotropes via Activation of a G-Protein-Coupled Receptor Pharmacologically Related to Both the NTS1 and nts2 Receptors of Mammals

Belmeguenaï¹,

Vaudry²,

Leprince³

et al. 2000

Neuroendocrinology

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The primary structure of frog neurotensin (fNT) has recently been determined and it has been shown that fNT is a potent stimulator of α-MSH secretion by frog pituitary melanotropes. In the present study, we have investigated the effects of fNT on the electrical activity of cultured frog melanotropes by using the patch-clamp technique and we have determined the pharmacological profile of the receptors mediating the effect of fNT. In the cell-attached configuration, fNT (10^–7 M) provoked an increase in the action current discharge followed by an arrest of spike firing. In the gramicidin-perforated patch configuration, fNT (10^–7 M) induced a depolarization accompanied by an increase in action potential frequency and a decrease in membrane resistance. Administration of graded concentrations (10^–10 to 10^–6 M) of fNT or the C-terminal hexapeptide NT(8–13) caused a dose-dependent increase in the frequency of action potentials with EC₅₀ of 2 × 10^–8 and 5 × 10^–9 M, respectively. The stimulatory effect of fNT was mimicked by various pseudopeptide analogs, with the following order of potency: Boc-[Trp¹¹]NT(8–13) > Boc-[D-Trp¹¹]NT(8–13) > Boc-[Lys^8,9, Nal¹¹]NT(8–13) > Boc-[Ψ11,12]NT(8–13). In contrast, the cyclic pseudopeptide analogs of NT(8–13), Lys-Lys-Pro-D-Trp-Ile-Leu and Lys-Lys-Pro-D-Trp-Glu-Leu-OH, did not affect the electrical activity. The NTS1 receptor antagonist and nts2 receptor agonist SR 48692 (10^–5 M) stimulated the spike discharge but did not block the response to fNT. In contrast, SR 142948A (10^–5 M), another NTS1 receptor antagonist and nts2 receptor agonist, inhibited the excitatory effect of fNT. The specific nts2 receptor ligand levocabastine (10^–6 M) had no effect on the basal electrical activity and the response of melanotropes to fNT. In cells which were dialyzed with guanosine-5′-O-(3-thiotriphosphate) (10^–4 M), fNT caused an irreversible stimulation of the action potential discharge. Conversely, dialysis of melanotropes with guanosine-5′-O-(2-thiodiphosphate) (10^–4 M) completely blocked the effect of fNT. Pretreatment of cells with cholera toxin (1 µg/ml) or pertussis toxin (0.2 µg/ml) did not affect the electrical response to fNT. Intracellular application of the G_o/i/s protein antagonist GPAnt-1 (3 × 10^–5 M) had no effect on the fNT-evoked stimulation. In contrast, dialysis of melanotropes with the G_q/11 protein antagonist GPAnt-2A (3 × 10^–5 M) abrogated the response to fNT. The present data demonstrate that fNT is a potent stimulator of the electrical activity of frog pituitary melanotropes. These results also reveal that the electrophysiological response evoked by fNT can be accounted for by activation of a G_q/11-protein-coupled receptor subtype whose pharmacological profile shares similarities with those of mammalian NTS1 and nts2 receptors.

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“…Frog pituitary melanotropes were cultured as previously described [35]. Briefly, neurointermediate lobes were dissociated by enzymatic and mechanical dispersion.…”

Section: Methodsmentioning

confidence: 99%

Neurotensin Modulates the Electrical Activity of Frog Pituitary Melanotropes via Activation of a G-Protein-Coupled Receptor Pharmacologically Related to Both the NTS1 and nts2 Receptors of Mammals

Belmeguenaï¹,

Vaudry²,

Leprince³

et al. 2000

Neuroendocrinology

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Distribution of the mRNAs encoding the thyrotropin‐releasing hormone (TRH) precursor and three TRH receptors in the brain and pituitary of Xenopus laevis: Effect of background color adaptation on TRH and TRH receptor gene expression

Bidaud

Galas

Bulant

et al. 2004

J of Comparative Neurology

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In amphibians, thyrotropin-releasing hormone (TRH) is a potent stimulator of alpha-melanotropin (alpha-MSH) secretion, so TRH plays a major role in the neuroendocrine regulation of skin-color adaptation. We have recently cloned a third type of TRH receptor in Xenopus laevis (xTRHR3) that has not yet been characterized in any other vertebrate species. In the present study, we have examined the distribution of the mRNAs encoding proTRH and the three receptor subtypes (xTRHR1, xTRHR2, and xTRHR3) in the frog CNS and pituitary, and we have investigated the effect of background color adaptation on the expression of these mRNAs. A good correlation was generally observed between the expression patterns of proTRH and xTRHR mRNAs. xTRHRs, including the novel receptor subtype xTRHR3, were widely expressed in the telencephalon and diencephalon, where two or even three xTRHR mRNAs were often simultaneously observed within the same brain structures. In the pituitary, xTRHR2 was expressed selectively in the distal lobe, and xTRHR3 was found exclusively in the intermediate lobe. Adaptation of frog skin to background illumination had no effect on the expression of proTRH and xTRHRs in the brain. In contrast, adaptation of the animals to a white background provoked an 18-fold increase in xTRHR3 mRNA concentration in the intermediate lobe of the pituitary. These data demonstrate that, in amphibians, the effect of TRH on alpha-MSH secretion is mediated through the novel receptor subtype xTRHR3.

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Evidence that urocortin I acts as a neurohormone to stimulate αMSH release in the toad Xenopus laevis

et al. 2005

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Involvement of Protein Kinase C and Protein Tyrosine Kinase in Thyrotropin-Releasing Hormone-Induced Stimulation ofα -Melanocyte-Stimulating Hormone Secretion in Frog Melanotrope Cells*

Cited by 10 publications

References 49 publications

Neurotensin Modulates the Electrical Activity of Frog Pituitary Melanotropes via Activation of a G-Protein-Coupled Receptor Pharmacologically Related to Both the NTS1 and nts2 Receptors of Mammals

Neurotensin Modulates the Electrical Activity of Frog Pituitary Melanotropes via Activation of a G-Protein-Coupled Receptor Pharmacologically Related to Both the NTS1 and nts2 Receptors of Mammals

Distribution of the mRNAs encoding the thyrotropin‐releasing hormone (TRH) precursor and three TRH receptors in the brain and pituitary of Xenopus laevis: Effect of background color adaptation on TRH and TRH receptor gene expression

Evidence that urocortin I acts as a neurohormone to stimulate αMSH release in the toad Xenopus laevis

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