We have used patch clamp techniques to study the enzymatic regulation of voltage-activated calcium channels in a rat pituitary tumor cell line. Previous work in this laboratory has established that these dihydropyridine-sensitive calcium channels only respond to depolarization when the protein(s) forming the channel are phosphorylated; in the absence of phosphorylation they are completely inactivated. Furthermore, the response to depolarization is specific to the kinase that acts on the channel: protein kinase C does not alter channel activity but the cAMP-dependent kinase produces short bursts of very brief openings and a calcium/calmodulin-dependent kinase produces long bursts of much longer openings. Two phosphatases have also been implicated in the regulation of these channels. The calcium/calmodulin-dependent phosphatase 2b, calcineurin, rapidly inactivates the channels when intracellular calcium concentration exceeds 1 (mu)M. In addition, recent studies with okadaic acid, the potent tumor promoter that is the major toxin in shellfish poisoning, have also implicated phosphatase 1 in calcium channel regulation. We are now beginning to characterize the role of these enzymes in calcium channel regulation dihydropyridines, compounds used clinically to treat stress-related human cardiovascular disease, and by hypothalamic neuropeptides that control pituitary hormone secretion. New evidence suggests that dihydropyridines produce their effects on these channels by altering their susceptibility to protein phosphorylation and its removal. In addition, we have shown that the GTP-dependent effects of neuropeptides reported widely in the literature do not result from direct interactions of GTP-binding proteins with the channels as suggested previously. Instead, the G proteins appear activate the kinases and phosphatases through conventional second messengers. These experiments are leading us to a molecular model of calcium channel function that will contribute to an understanding of the toxicity of environmental hazards.
| Lucas, Sarah J; Armstrong, David L (2015) Protein phosphatase modulation of somatostatin receptor signaling in the mouse hippocampus. Neuropharmacology 99:232-41 |
| Chatterjee, Anindya; Wang, Ling; Armstrong, David L et al. (2010) Activated Rac1 GTPase translocates protein phosphatase 5 to the cell membrane and stimulates phosphatase activity in vitro. J Biol Chem 285:3872-82 |
| Armstrong, David L; Erxleben, Christian; White, Jody A (2010) Patch clamp methods for studying calcium channels. Methods Cell Biol 99:183-97 |
| Sanchez-Ortiz, Efrain; Hahm, Byoung Kwon; Armstrong, David L et al. (2009) Protein phosphatase 5 protects neurons against amyloid-beta toxicity. J Neurochem 111:391-402 |
| Liao, Yanhong; Erxleben, Christian; Yildirim, Eda et al. (2007) Orai proteins interact with TRPC channels and confer responsiveness to store depletion. Proc Natl Acad Sci U S A 104:4682-7 |
| Erxleben, Christian; Liao, Yanhong; Gentile, Saverio et al. (2006) Cyclosporin and Timothy syndrome increase mode 2 gating of CaV1.2 calcium channels through aberrant phosphorylation of S6 helices. Proc Natl Acad Sci U S A 103:3932-7 |
| Gentile, Saverio; Darden, Thomas; Erxleben, Christian et al. (2006) Rac GTPase signaling through the PP5 protein phosphatase. Proc Natl Acad Sci U S A 103:5202-6 |
| Storey, Nina M; Gomez-Angelats, Mireia; Bortner, Carl D et al. (2003) Stimulation of Kv1.3 potassium channels by death receptors during apoptosis in Jurkat T lymphocytes. J Biol Chem 278:33319-26 |
| Erxleben, Christian; Gomez-Alegria, Claudio; Darden, Thomas et al. (2003) Modulation of cardiac Ca(V)1.2 channels by dihydropyridine and phosphatase inhibitor requires Ser-1142 in the domain III pore loop. Proc Natl Acad Sci U S A 100:2929-34 |
| Tian, Lijun; Coghill, Lorraine S; MacDonald, Stephen H-F et al. (2003) Leucine zipper domain targets cAMP-dependent protein kinase to mammalian BK channels. J Biol Chem 278:8669-77 |
Showing the most recent 10 out of 19 publications
