Protein-tyrosine kinases activate while protein-tyrosine phosphatases inhibit L-type calcium channel activity in pituitary GH3 cells.
The aim of this study was to evaluate the effect of protein-tyrosine kinase (PTK) and protein tyrosine phosphatase (PTP) inhibitors on Ca2+ channels in GH3 cells. The activity of Ca2+ channels was monitored either by single-cell microfluorometry or by the whole-cell configuration of the patch-clamp technique. Genistein (20-200 micron) and herbimycin A (1-15 micron) inhibited [Ca2+]i rise induced either by 55 mM K+ or 10 micron Bay K 8644. In addition, genistein and lavendustin A inhibited whole-cell Ba2+ currents. By contrast, daidzein, a genistein analogue devoid of PTK inhibitory properties, did not modify Ca2+ channel activity. The inhibitory action of genistein on the [Ca2+]i increase was completely counteracted by the PTP inhibitor vanadate (100 micron). Furthermore, vanadate alone potentiated -Ca2+-i response to both 55 mM K+ and 10 micron Bay K 8644. The possibility that genistein could decrease the [Ca2+]i elevation by enhancing Ca2+ removal from the cytosol seems unlikely since genistein also reduced the increase in fura-2 fluorescence ratio induced by Ba2+, a cation that enters into the cells through Ca2+ channels but cannot be pumped out by Ca2+ extrusion mechanisms. Finally, in unstimulated GH3 cells, genistein caused a decline of [Ca2+]i and the disappearance of [Ca2+]i oscillations, whereas vanadate induced an increase of [Ca2+]i and the appearance of [Ca2+]i oscillations in otherwise non-oscillating cells. The present results suggest that in GH3 cells PTK activation causes an increase of L-type Ca2+ channel function, whereas PTPs exert an inhibitory role.
Cataldi
M
M
Section of Pharmacology, Department of Neurosciences, University of Naples Federico II, Naples, Italy.
Taglialatela
M
M
Guerriero
S
S
Amoroso
S
S
Lombardi
G
G
di Renzo
G
G
Annunziato
L
L
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D016227:Benzoquinones; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020746:Calcium Channels, L-Type; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D019833:Genistein; D007529:Isoflavones / Q000494:pharmacology; D007700:Kinetics; D047029:Lactams, Macrocyclic; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D010636:Phenols / Q000494:pharmacology; D010902:Pituitary Gland; D010911:Pituitary Neoplasms; D011188:Potassium / Q000494:pharmacology; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011809:Quinones / Q000494:pharmacology; D017828:Rifabutin / Q000031:analogs & derivatives; D013997:Time Factors
D016227:Benzoquinones; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D007529:Isoflavones; D047029:Lactams, Macrocyclic; D010636:Phenols; D011809:Quinones; D017828:Rifabutin; D001464:Barium; C062898:lavendustin A; C004742:daidzein; C020754:herbimycin; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D019833:Genistein; D011505:Protein-Tyrosine Kinases; D017027:Protein Tyrosine Phosphatases; D011188:Potassium; D002118:Calcium