dibutyryl-cyclic-gmp and vinpocetine

Double sucrose gap experiments were carried out to study the effect of phosphodiesterase inhibitors and penetrating analogs of cyclic nucleotides on action potential and contraction of guinea pig ureteral smooth muscle cells. 3-Isobutyl-1-methylxanthine (10 microM) and dibutyryl-cAMP (20 microM) shortened the plateau of action potential and inhibited contraction of smooth muscle cells by increasing potassium permeability of their membrane. Vinpocetine (1 microM) and dibutyryl-cAMP (100 microM) strengthened contraction of smooth muscle cells and shortened action potentials by decreasing sodium permeability of their membrane.

Topics: 1-Methyl-3-isobutylxanthine; 3',5'-Cyclic-AMP Phosphodiesterases; 3',5'-Cyclic-GMP Phosphodiesterases; Action Potentials; Animals; Bucladesine; Dibutyryl Cyclic GMP; Enzyme Inhibitors; Female; Guinea Pigs; In Vitro Techniques; Muscle Contraction; Muscle, Smooth; Uterus; Vinca Alkaloids

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 GH3 cells using fura-2 single cell videoimaging. Vinpocetine (2.5-50 microM), 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 N2,2'-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 GH3 cells may be regulated by the activity of type I PDE-cGMP-PKG pathway.

Topics: Alkaloids; Animals; Calcium; Carbazoles; Cell Line; Cyclic AMP; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Cyclic Nucleotide Phosphodiesterases, Type 1; Dibutyryl Cyclic GMP; Enzyme Inhibitors; Indoles; Phosphoric Diester Hydrolases; Pituitary Gland; Protein Kinases; Pyrroles; Vinca Alkaloids

High-threshold transient K+ current (IAht) was recorded using a two-microelectrode voltage clamp technique in isolated neurons of the land snail. Effect of the nootropic drug vinpocetine on this current was studied and compared with cyclic nucleotides. The drug either enhanced or left unaltered the IAht, and dibutyryl cyclic GMP (dcGMP) imitated the effect. These two effects were not additive. Dibutyryl cyclic AMP did not imitate, the vinpocetine effect and decreased the amplitude of the IAht. The findings suggest that the cGMP mediated the vinpocetine effect on the Iaht.

Topics: Animals; Bucladesine; Cyclic GMP; Dibutyryl Cyclic GMP; Helix, Snails; In Vitro Techniques; Neurons; Nootropic Agents; Patch-Clamp Techniques; Potassium Channels; Vinca Alkaloids