Thrombin-stimulated increases in cytosolic Ca2+ level and gonadotropin-releasing hormone release in GT1-7 neurons

The effects of thrombin on cytosolic calcium levels ([Ca2+](cyt)), and on g onadotropin-releasing hormone (GnRH) release, were characterized in culture d GT1-7 neurons. GnRH release from GT1-7 neurons was pulsatile with an aver age pulse amplitude of 14.3 +/- 5.8 pg . min . ml(-1) and an average pulse duration of 21.3 +/- 4.2 min. The [Ca2+](cyt) response to 0.005 to 0.2 U/ml thrombin was saturable and concentration dependent (EC50 = 0.0268 U/ml). E thyleneglycotetraacetic acid (EGTA) chelation of extracellular Ca2+ resulte d in an approximate to 70% attenuation of thrombin-stimulated increase in [ Ca2+](cyt). By use of a special superfusion system, a 5-min exposure to 0.1 U/ml thrombin significantly increased the amplitude (193.2 +/- 67.8 pg . m in . ml(-1); P = 0.001) but not the duration (22.5 +/- 2.4 min; P = 0.8) of GnRH release. These results suggest that thrombin increases [Ca2+](cyt) an d GnRH release from GT1-7 neurons via specific membrane-bound receptors. (C ) 1999 Elsevier Science Inc. All rights reserved.