Title

Cloning and characterization of a calcitonin receptor from the guinea pig brain

Date of Award

1998

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Physiology and Biophysics

First Committee Member

Ian M. Dickerson, Committee Chair

Abstract

Calcitonin is a 32 amino acid peptide hormone of neural crest origin secreted by the parafollicular cells of the thyroid. It is believed that calcitonin, through specific and high affinity interactions with the calcitonin receptor, mediates a diverse spectrum of effective such as hypocalcemia, analgesia, anorexia, suppression of gastric acid secretion, and inhibition of prolactin secretion. However, which of these actions represents the true physiologic role for calcitonin has not been clearly defined. To better understand the physiology of calcitonin and calcitonin receptors, a calcitonin receptor was cloned from a guinea pig brain using a degenerate reverse transcription/polymerase chain reaction (RT/PCR) strategy. Sequence analysis of this receptor showed that it contains 478 amino acids and is a member of the seven transmembrane G-protein coupled receptor superfamily. COS 1 cells transfected with the cloned guinea pig calcitonin receptor cDNA and activated by salmon calcitonin produced a 10 fold increase in intracellular cAMP accumulation, EC$\sb{50}$ of 0.1 nM. In this system, human calcitonin was $>250$ fold less potent and the related neuropeptides, rat $\alpha$CGRP and rat amylin, did not activate the guinea pig calcitonin receptor at physiological concentrations. Stimulation of the guinea pig calcitonin receptor in transfected cells by salmon calcitonin resulted in $>2$ fold increase in phosphatidylinositol hydrolysis with an EC$\sb{50}$ of 2.5 nM. A PCR based strategy to detect possible subtypes of the guinea pig calcitonin receptor revealed that guinea pigs express a single calcitonin receptor subtype. Such a finding contrasts previous observations that other calcitonin receptors from different species contain multiple receptor subtypes. This may indicate that the other subtypes of calcitonin receptors may not have a primary role in calcitonin biology but rather represent species specific modifications of the calcitonin receptor. Tissue distribution of the guinea pig calcitonin receptor was determined by a combination of RT/PCR, Northern analysis, and expression in Xenopus oocytes. These studies consistently demonstrated that the guinea pig calcitonin receptors have the highest expression in the diencephalon. The abundance of calcitonin receptors in the guinea pig brain suggests that this receptor may participate in regulating some functions of the central nervous system, such as analgesia and anorexia.

Keywords

Biology, Molecular; Biology, Neuroscience

Link to Full Text

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