Protein-tyrosine Kinases Activate while Protein-tyrosine Phosphatases Inhibit L-type Calcium Channel Activity in Pituitary
GH
Cells (*)
- Mauro Cataldi,
- Maurizio Taglialatela,
- Salvatore Guerriero,
- Salvatore Amoroso,
- Gaetano Lombardi,
- Gianfranco di Renzo(1) and
- Lucio Annunziato(§)
- From the Section of Pharmacology, Department of Neurosciences, University of Naples Federico II, 80131 Naples, Italy and the
- School of Pharmacy, University of Catanzaro, 88021 Catanzaro, Italy
- §To whom correspondence should be addressed: Section of Pharmacology, Dept. of Neurosciences, University of Naples Federico II, Via S. Pansini, 5, 80131 Naples, Italy. Tel.: 39-81-746-3323; Fax: 39-81-746-3323; farmacol{at}ds.cised.unina.it.
Abstract
The aim of this study was to evaluate the effect of protein-tyrosine kinase (PTK) and protein tyrosine phosphatase (PTP) inhibitors
on Ca
channels in GH
cells. The activity of Ca
channels was monitored either by single-cell microfluorometry or by the whole-cell configuration of the patch-clamp technique.
Genistein (20-200 μM) and herbimycin A (1-15 μM) inhibited [Ca
]
rise induced either by 55 mM K
or 10 μM Bay K 8644. In addition, genistein and lavendustin A inhibited whole-cell Ba
currents. By contrast, daidzein, a genistein analogue devoid of PTK inhibitory properties, did not modify Ca
channel activity. The inhibitory action of genistein on the [Ca
]
increase was completely counteracted by the PTP inhibitor vanadate (100 μM). Furthermore, vanadate alone potentiated [Ca
]
response to both 55 mM K
and 10 μM Bay K 8644. The possibility that genistein could decrease the [Ca
]
elevation by enhancing Ca
removal from the cytosol seems unlikely since genistein also reduced the increase in fura-2 fluorescence ratio induced by
Ba
, a cation that enters into the cells through Ca
channels but cannot be pumped out by Ca
extrusion mechanisms. Finally, in unstimulated GH
cells, genistein caused a decline of [Ca
]
and the disappearance of [Ca
]
oscillations, whereas vanadate induced an increase of [Ca
]
and the appearance of [Ca
]
oscillations in otherwise non-oscillating cells. The present results suggest that in GH
cells PTK activation causes an increase of L-type Ca
channel function, whereas PTPs exert an inhibitory role.
Footnotes
-
↵* This work was supported by Consiglio Nazionale delle Ricerche Grants 93.02003-CT14, 93.04222-CT04, and 94.02525-CT04 and Ministero dell' Università e della Ricerca Scientifica e Tecnologica (by 40 and 60% grants) (to L. A. and G. d. R.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
-
↵1 The abbreviations used are:
- PKA
-
protein kinase A
- PKC
-
protein kinase C
- PTK
-
protein tyrosine kinase
- [Ca
]
-
cytosolic free calcium
- PTP
-
protein tyrosine phosphatase
- fura-2/AM
-
fura-2 acetoxymethylester.
-
- Received June 13, 1995.
- Revision received February 1, 1996.
- © 1996 by The American Society for Biochemistry and Molecular Biology, Inc.
