Heterozygous gsp mutation renders ion channels of human somatotroph adenoma cells unresponsive to growth hormone-releasing hormone.
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.
Yasufuku-Takano
J
J
Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan. jytakano-tky@umin.ac.jp
Takano
K
K
Takei
T
T
Fukumoto
S
S
Teramoto
A
A
Takakura
K
K
Yamashita
N
N
Fujita
T
T
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000236:Adenoma / Q000235:genetics / Q000503:physiopathology*; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology; D002412:Cations; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004553:Electric Conductivity; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000235:genetics*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D006579:Heterozygote; D019382:Human Growth Hormone / Q000378:metabolism*; D006801:Humans; D015640:Ion Channel Gating; D007473:Ion Channels / Q000187:drug effects*; D009154:Mutation; D010911:Pituitary Neoplasms / Q000235:genetics / Q000503:physiopathology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D002412:Cations; D004791:Enzyme Inhibitors; D007473:Ion Channels; D019382:Human Growth Hormone; D015124:8-Bromo Cyclic Adenosine Monophosphate; D013007:Growth Hormone-Releasing Hormone; D017868:Cyclic AMP-Dependent Protein Kinases; D019205:GTP-Binding Protein alpha Subunits, Gs; D002118:Calcium