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TRPM8-Dependent Dynamic Response in a Mathematical Model of Cold Thermoreceptor.

ABSTRACT: Cold-sensitive nerve terminals (CSNTs) encode steady temperatures with regular, rhythmic temperature-dependent firing patterns that range from irregular tonic firing to regular bursting (static response). During abrupt temperature changes, CSNTs show a dynamic response, transiently increasing their firing frequency as temperature decreases and silencing when the temperature increases (dynamic response). To date, mathematical models that simulate the static response are based on two depolarizing/repolarizing pairs of membrane ionic conductance (slow and fast kinetics). However, these models fail to reproduce the dynamic response of CSNTs to rapid changes in temperature and notoriously they lack a specific cold-activated conductance such as the TRPM8 channel. We developed a model that includes TRPM8 as a temperature-dependent conductance with a calcium-dependent desensitization. We show by computer simulations that it appropriately reproduces the dynamic response of CSNTs from mouse cornea, while preserving their static response behavior. In this model, the TRPM8 conductance is essential to display a dynamic response. In agreement with experimental results, TRPM8 is also needed for the ongoing activity in the absence of stimulus (i.e. neutral skin temperature). Free parameters of the model were adjusted by an evolutionary optimization algorithm, allowing us to find different solutions. We present a family of possible parameters that reproduce the behavior of CSNTs under different temperature protocols. The detection of temperature gradients is associated to a homeostatic mechanism supported by the calcium-dependent desensitization.

SUBMITTER: Olivares E

PROVIDER: S-EPMC4591370 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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TRPM8-Dependent Dynamic Response in a Mathematical Model of Cold Thermoreceptor.

Olivares Erick E Salgado Simón S Maidana Jean Paul JP Herrera Gaspar G Campos Matías M Madrid Rodolfo R Orio Patricio P

PloS one 20151001 10

Cold-sensitive nerve terminals (CSNTs) encode steady temperatures with regular, rhythmic temperature-dependent firing patterns that range from irregular tonic firing to regular bursting (static response). During abrupt temperature changes, CSNTs show a dynamic response, transiently increasing their firing frequency as temperature decreases and silencing when the temperature increases (dynamic response). To date, mathematical models that simulate the static response are based on two depolarizing/ ...[more]

PMID: 26426259

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Project description:Highlights • Tunica dartos smooth muscle (TDSM), which is responsible for scrotal thermoregulation, responds to cooling by enhancement of basal tension, and increase of the amplitude and duration of synaptically-evoked contractions.• TDSM cold-induced tension, but not synaptically-evoked contractions are sensitive to the blockers of TRPM8 cold/menthol receptor.• TRPM8 is localized to the TDSM cells' endoplasmic reticulum and its activation by cold causes intracellular calcium mobilization.• Chemical castration of male rats consequent to pharmacological blockade of androgen receptors eliminates the effects of cold on TDSM tension, but not on synaptically-evoked contractions, and abolishes TRPM8 protein expression.• TRPM8 is an important determinant of cold-dependent contractility of the tunica dartos muscle and scrotal thermoregulation which is crucial for maintaining normal spermatogenesis and male fertility. Tunica dartos smooth muscle (TDSM) lies beneath the scrotal skin, and its contraction leads to scrotum wrinkling upon cooling. However, neither the nature of TDSM cold-sensitivity nor the underlying molecular sensors are well understood. Here we have investigated the role of cold/menthol-sensitive TRPM8 channel in TDSM temperature-dependent contractility. The contraction of isolated male rat TDSM strips was studied by tensiometry. TRPM8 expression was assayed by RT-PCR and fluorescence immunochemistry. Isolated TDSM strips responded to cooling from 33 °C to 20 °C by enhancement of basal tension, and increase of the amplitude and duration of electric field stimulated (EFS) contractions. The effects of cold on basal tension, but not on EFS-contractions, could be 80% inhibited by TRPM8 blockers, capsazepine and BCTC [N-(4‑tert-butylphenyl)-4-(3-chloropyridin-2-yl)piperazine-1-carboxamide], and could be partially mimicked by menthol. RT-PCR and immunolabeling showed TRPM8 mRNA and protein expression in TDSM cells with protein labelling being predominantly localized to intracellular compartments. Chemical castration of male rats consequent to the treatment with androgen receptor blocker, flutamide, led to the abrogation of cold effects on TDSM basal tension, but not on EFS-contractions, and to the disappearance of TRPM8 protein expression. We conclude that TRPM8 is involved in the maintenance of basal cold-induced TDSM tonus, but not in sympathetic nerve-mediated contractility, by acting as endoplasmic reticulum Ca2+ release channel whose expression in TDSM cells requires the presence of a functional androgen receptor. Thus, TRPM8 plays a crucial role in scrotal thermoregulation which is important for maintaining normal spermatogenesis and male fertility.

Dataset Information

TRPM8-Dependent Dynamic Response in a Mathematical Model of Cold Thermoreceptor.

Publications

TRPM8-Dependent Dynamic Response in a Mathematical Model of Cold Thermoreceptor.

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