Growth hormone releasing hormone (grf) augments the voltage-gated sodium current in cultured rat pituitary cells. Kato, Masakatsu. Department of Physiology, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi 371 Japan
APStracts 2:0274C, 1995.
The effect of human growth hormone releasing hormone (hGRF), a potent stimulator of adenylate cyclase in somatotrophs, on the voltage-gated sodium current was determined by perforated patch clamp of cultured rat somatotrophs. The amplitude of the voltage-gated sodium current was augmented by 65.3 +/- 20.6% (mean +/- SEM, n=7) by 10 nM hGRF. This augmentation was reversibly blocked by 10 [mu]M H-89, a specific inhibitor for adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase. Membrane permeant analogue of cAMP, dibutyryl cAMP (DBcAMP, 5 mM) also augmented the voltage-gated sodium current by 39.6+/- 7.4% (n=10). There were no effects of hGRF or DBcAMP on a steady-state inactivation of the sodium current. In contrast, in the whole-cell configuration of patch clamp, no augmentation of the sodium current was observed either by hGRF or by membrane permeant analogue of cAMP. These results suggest that hGRF augmented the peak amplitude of the voltage-gated sodium current in rat somatotrophs via phosphorylation by cyclic AMP-dependent protein kinase. For this augmentation, the intracellular environment must be kept in relatively intact condition. 

Received 22 February 1995; accepted in final form 28 June 1995.
APS Manuscript Number C97-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.