RESUMO
The Ca2+ receptor is a G protein-coupled receptor that enables parathyroid cells and certain other cells in the body to respond to changes in the level of extracellular Ca2+. The Ca2+ receptor is a member of a family of G protein-coupled receptors that includes metabotropic glutamate receptors (mGluRs), gamma-aminobutyric acidB receptors, and putative pheromone receptors. As a family, these receptors are characterized by limited sequence homology and an unusually large putative extracellular domain (ECD). The ECD of the mGluRs is believed to determine agonist selectivity, but the functions of the structural domains of the Ca2+ receptor are not known. To identify structural determinants for cation recognition and activation of the Ca2+ receptor (and to further study the mGluRs), two chimeric receptors were constructed in which the large ECD of the Ca2+ receptor and the mGluR1 were interchanged. When expressed in Xenopus laevis oocytes, one of these chimeras, named CaR/mGluR1 [ECD of the Ca2+ receptor and transmembrane domain (TMD) of the mGluR1], responded to cation agonists (Gd3+, Ca2+, neomycin) of the Ca2+ receptor at concentrations similar to those necessary for activation of the native Ca2+ receptor. A reciprocal construct, named mGluR1/CaR (ECD of the mGluR1 and TMD of the Ca2+ receptor), was responsive to mGluR agonists but was much less sensitive to two of three cation agonists known to activate the Ca2+ receptor. A deletion construct of the Ca2+ receptor (DeltantCaR), which lacked virtually the entire ECD, was only activated by one of three agonists tested. These results suggest that the primary determinants for agonist activation of both the Ca2+ receptor and the mGluRs are found in the large ECD and that the Ca2+ receptor is possibly distinguished from the mGluRs in that it may contain sites in the TMD that permit activation by certain cation agonists.
Assuntos
Proteínas de Ligação ao Cálcio/química , Animais , Sítios de Ligação , Proteínas de Ligação ao Cálcio/agonistas , Proteínas de Ligação ao Cálcio/genética , Proteínas de Ligação ao Cálcio/metabolismo , Ligantes , Oócitos/fisiologia , Conformação Proteica , Receptores de Glutamato Metabotrópico/agonistas , Receptores de Glutamato Metabotrópico/genética , Receptores de Glutamato Metabotrópico/metabolismo , Proteínas Recombinantes de Fusão/agonistas , Proteínas Recombinantes de Fusão/metabolismo , Xenopus laevisRESUMO
Parathyroid hormone (PTH) release is regulated by extracellular calcium through a Ca2+ receptor (CaR) located on the surface of the parathyroid cell. With advancing age, the serum concentration of PTH increases, and evidence suggests that the calcium set-point for PTH release may also increase. To determine whether these changes are linked to a change in CaR expression, we quantitated mRNA and protein for the receptor in parathyroid glands of 6-week-, 6-month- and 24-month-old rats. Thyroid and kidney tissue were also studied. Between 6 weeks and 24 months of age, CaR mRNA in the parathyroid gland increased 11.4- and 3.3-fold as measured by competitive reverse transcription PCR and solution hybridization assays respectively. Message levels for the receptor also increased in the thyroid but not in the kidney. Coincident with the increase in message levels, receptor protein concentration in the parathyroid increased 7-fold between 6 weeks and 24 months of age. These results suggest that the altered relationship between extracellular calcium and PTH release observed in aging is associated with dramatic changes in CaR metabolism. That PTH secretion is increased despite increased receptor concentration suggests that aging may impair calcium binding or coupling between the CaR and down-stream effector elements in the pathway regulating PTH release.
Assuntos
Envelhecimento/metabolismo , Cálcio/metabolismo , Glândulas Paratireoides/metabolismo , RNA Mensageiro/metabolismo , Receptores de Superfície Celular/metabolismo , Animais , Western Blotting , Cátions , Hibridização In Situ , Masculino , Reação em Cadeia da Polimerase , Ratos , Ratos Endogâmicos F344 , Receptores de Superfície Celular/genética , Processamento de Sinais Assistido por ComputadorRESUMO
The use of physiological measurements, heart rate and oral temperature, for evaluating a heat stress situation in an industrial plant is described. In contrast to evaluation of hot jobs by environmental measurements and subjective evaluation of metabolic rate, the technique used with the WBGT criteria, evaluation of heat strain by measurements of the individual's heart rate and oral temperature is simpler, less expensive, less restrictive and more protective. A description of the technique involved for an industrial job along with suggested heart rate recovery criteria are included.
