Augmentation of transient low-threshold Ca2+ current induced by GTP-binding protein signal transduction system in GH3 pituitary cells.
We characterized the effects of thyrotropin-releasing hormone (TRH; 500 nM) and guanosine 5'-0-3-thiotriphosphate (GTP gamma S; 50 microM) on two types of Ca2+ currents in pituitary-hormone-secretory GH3 cells and were surprised to find marked increases in transient, low-threshold Ca2+ currents (T currents) induced by extracellularly applied TRH or intracellularly applied GTP gamma S. The effect of TRH was blocked by intracellularly applied guanosine 5'-0-2-thiodiphosphate (GDP beta S; 100 microM). The increase in the T current was found to be accompanied by a decrease in long-lasting, high-threshold Ca2+ current (L-current), in response to both TRH or GTP gamma S. These indicate that the enhancement of Ca2+ influx by TRH (500 nM) is largely conferred by T currents in GH3 cells. A reduced concentration of TRH (5 nM) still markedly increased the T current, but failed to decrease the L current. These data suggest that the augmentation of the T currents as well as depression of the L currents by TRH (500 nM), through the activation of a GTP-binding protein, may constitute an important regulatory mechanism of sustained pituitary hormone secretion in GH3 cells.
Suzuki
N
N
Department of Physiology, School of Medicine, Kitasato University, Kanagawa, Japan.
Takagi
H
H
Yoshioka
T
T
Tanakadate
A
A
Kano
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004553:Electric Conductivity; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D010911:Pituitary Neoplasms; D051381:Rats; D015398:Signal Transduction / Q000502:physiology*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D016244:Guanosine 5'-O-(3-Thiotriphosphate); D013973:Thyrotropin-Releasing Hormone; D019204:GTP-Binding Proteins; D002118:Calcium