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  • Title: Heterozygous gsp mutation renders ion channels of human somatotroph adenoma cells unresponsive to growth hormone-releasing hormone.
    Author: Yasufuku-Takano J, Takano K, Takei T, Fukumoto S, Teramoto A, Takakura K, Yamashita N, Fujita T.
    Journal: Endocrinology; 1999 May; 140(5):2018-26. PubMed ID: 10218950.
    Abstract:
    Ionic mechanisms play an important role in the regulation of hormone secretion. The GHRH-induced GH release by human GH-secreting cells is transmitted through protein kinase A (PKA), which activates nonselective cation current (NSCC) and induces membrane depolarization, intracellular Ca2+ increase, and GH secretion. To evaluate whether ionic mechanisms have pathophysiological significance in GH oversecretion of GH-secreting pituitary adenomas, we examined four adenomas with constitutively active Gs alpha mutation (gsp mutation) and compared with three gsp-negative adenomas. In primary-cultured cells of gsp-positive adenomas, GHRH did not increase the NSCC under voltage-clamp experiments. Detailed examination showed that NSCC was maximally activated at the basal level and application of GHRH did not increase the current in these adenomas. Furthermore, by using single-cell RT-PCR method, we demonstrated for the first time at the single cell level that gsp mutation is heterozygous in GH-secreting pituitary adenomas. These indicate that heterozygous gsp mutation fully activates NSCC at the basal level, which may account for the GH oversecretion in gsp-positive GH-secreting pituitary adenomas.
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