Involvement of phosphodiesterase-cGMP-PKG pathway in intracellular Ca2+ oscillations in pituitary GH3 cells

The present study investigates the potential role of the Ca2+-calmodulin-dependent type I phosphodiesterase (PDE)-cGMP-protein kinase G (PKG) pathway in spontaneous [Ca2+](i) oscillations in GH(3) cells using fura-2 single cell videoimaging. Vinpocetine (2.5-50 mu M), a selective inhibitor of type I PDE, induced a concentration-dependent inhibition of spontaneous [Ca2+](i) oscillations in these pituitary cells, and at the same time produced an increase of the intracellular cGMP content. The cell permeable cGMP analog N-2,2'-O-dibutyryl-cGMP (dB-cGMP) (1 mM) caused a progressive reduction of the frequency and the amplitude of spontaneous [Ca2+](i) oscillations when added to the medium. KT5823 (400 nM), a selective inhibitor of cGMP-dependent protein kinase (PKG), produced an increase of baseline [Ca2+](i) and the disappearance of spontaneous [Ca2+](i) oscillations. When KT5823 was added before vinpocetine, the PKG inhibitor counteracted the [Ca2+](i) lowering effect of the cGMP catabolism inhibitor. Finally, the removal of extracellular Ca2+ or the blockade of L-type voltage-sensitive calcium channels (VSCC) by nimodipine produced a decrease of cytosolic cGMP levels. Collectively, the results of the present study suggest that spontaneous [Ca2+](i) oscillations in GH(3) cells may be regulated by the activity of type I PDE-cCMP-PKG pathway. (C) 1999 Published by Elsevier Science B.V. All rights reserved.