Augmentation of transient low-threshold Ca^2^+ current induced by GTP-binding protein signal transduction system in GH"3 pituitary cells - Suzuki, N.; Takagi, H.; Yoshioka, T.; Tanakadate, A.; Kano, M. (Elsevier)
We characterized the effects of thyrotropin-releasing hormone (TRH; 500 nM) and guanosine 5'-0-3-thiotriphosphate (GTP γ S; 50 μM) on two types of Ca^2^+ currents in pituitary-hormone-secretory GH"3 cells and were surprised to find marked increases in transient, low-threshold Ca^2^+ currents (T currents) induced by extracellularly applied TRH or intracellularly applied GTP γ S. The effect of TRH was blocked by intracellularly applied guanosine 5'-0-2-thiodiphosphate (GDP βS; 100 μM). The increase in the T current was found to be accompanied by a decrease in long-lasting, high-threshold Ca^2^+ current (L-current), in response to both TRH or GTP γ S. These indicate that the enhancement of Ca^2^+ influx by TRH (500 nM) is largely conferred by T currents in GH"3 cells. A reduced conceptration 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 GH"3 cells.
http://dx.doi.org/10.1016/S0006-291X(05)81526-8
Keywords: W; V; U