AJP - Cell Physiology, Vol 270, Issue 1 C125-C130, Copyright © 1996 by American Physiological Society
Growth hormone-releasing hormone augments voltage-gated Na+ current in cultured rat pituitary cells
M. Kato
Department of Physiology, Gunma University, Maebashi, Japan.
The effect of human growth hormone-releasing hormone (hGHRH), 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 +/- SE, n = 7) by 10 nM hGHRH. This
augmentation was reversibly blocked by 10 microM H-89 a specific inhibitor
for adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase.
The membrane-permeant analogue of cAMP, dibutyryl cAMP (5 mM), also
augmented the voltage-gated sodium current by 39.6 +/- 7.4% (n = 10). There
were no effects of hGHRH or dibutyryl cAMP on 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 by hGHRH or by
the membrane-permeant analogue of cAMP. These results suggest that hGHRH
augments the peak amplitude of the voltage-gated sodium current in rat
somatotrophs via phosphorylation by cAMP-dependent protein kinase. For this
augmentation, the intracellular environment must be kept relatively intact.
