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. 1995 Sep 1;487(Pt 2):291–303. doi: 10.1113/jphysiol.1995.sp020880

Residual Ca2+ channel current modulation by megestrol acetate via a G-protein alpha s-subunit in rat hypothalamic neurones.

A M Costa 1, K T Spence 1, C R Plata-Salamán 1, J M ffrench-Mullen 1
PMCID: PMC1156573  PMID: 8558464

Abstract

1. The inhibition of voltage-activated Ca2+ channel currents by the orally active progesterone derivative, megestrol acetate (MA), was examined in freshly dissociated rat ventromedial hypothalamic nucleus (VMN) neurones using the whole-cell voltage-clamp technique with 10 mM Ba2+ as the charge carrier. 2. The steady-state inhibition of the peak high-threshold Ca2+ channel current evoked by depolarization from -80 to -10 mV by MA increased in a concentration-dependent fashion. MA inhibited a fraction of the whole-cell Ca2+ channel current while progesterone had no effect on the peak Ca2+ channel current (7% at 10 microM). The low-threshold Ca2+ (T-type) current, evoked from -100 to -30 mV, was unaffected by MA. 3. Intracellular dialysis with MA had no effect on the Ca2+ channel current. Concomitant extracellular perfusion of MA showed normal inhibitory activity, suggesting that the MA binding site can only be accessed extracellularly. 4. The high-threshold Ca2+ channel current in VMN neurones was found to consist of four pharmacologically distinguishable components: an N-type current, an L-type current, a P-type current, and a residual current. MA had no effect on the N-, L- and P-type Ca2+ channel currents, but inhibited the residual current. 5. In neurones isolated from cholera toxin-treated animals, the MA-induced inhibition of the Ca2+ channel current was significantly diminished, suggesting a G-protein alpha S-subunit involvement. 6. Treatment with antisense phosphothio-oligodeoxynucleotides to the G alpha S-subunit (antisense-G alpha S) significantly reduced the MA-induced inhibition of the Ca2+ channel current. Treatment with either sense-G alpha S or antisense-G alpha 11 had no effect, confirming a G alpha S-subunit involvement. 7. These results suggest that appetite enhancement induced by MA in cachectic patients may in part be due to a novel central nervous system action, that is, inhibition of a fraction of the whole-cell Ca2+ channel current to attenuate the firing of VMN neurones that may be involved in satiety mechanisms.

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Selected References

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  1. Aisner J., Tchekmedyian N. S., Moody M., Tait N. High-dose megestrol acetate for the treatment of advanced breast cancer: dose and toxicities. Semin Hematol. 1987 Apr;24(2 Suppl 1):48–55. [PubMed] [Google Scholar]
  2. Akaike N., Kostyuk P. G., Osipchuk Y. V. Dihydropyridine-sensitive low-threshold calcium channels in isolated rat hypothalamic neurones. J Physiol. 1989 May;412:181–195. doi: 10.1113/jphysiol.1989.sp017610. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Bell R. M., Burns D. J. Lipid activation of protein kinase C. J Biol Chem. 1991 Mar 15;266(8):4661–4664. [PubMed] [Google Scholar]
  4. Bertrand D., Valera S., Bertrand S., Ballivet M., Rungger D. Steroids inhibit nicotinic acetylcholine receptors. Neuroreport. 1991 May;2(5):277–280. doi: 10.1097/00001756-199105000-00016. [DOI] [PubMed] [Google Scholar]
  5. Bielajew C., Stenger J., Schindler D. Factors that contribute to the reduced weight gain following chronic ventromedial hypothalamic stimulation. Behav Brain Res. 1994 Jun 30;62(2):143–148. doi: 10.1016/0166-4328(94)90021-3. [DOI] [PubMed] [Google Scholar]
  6. Bruera E. Current pharmacological management of anorexia in cancer patients. Oncology (Williston Park) 1992 Jan;6(1):125-30; discussion 132, 137. [PubMed] [Google Scholar]
  7. Carbone E., Swandulla D. Neuronal calcium channels: kinetics, blockade and modulation. Prog Biophys Mol Biol. 1989;54(1):31–58. doi: 10.1016/0079-6107(89)90008-4. [DOI] [PubMed] [Google Scholar]
  8. Cassel D., Selinger Z. Mechanism of adenylate cyclase activation by cholera toxin: inhibition of GTP hydrolysis at the regulatory site. Proc Natl Acad Sci U S A. 1977 Aug;74(8):3307–3311. doi: 10.1073/pnas.74.8.3307. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Cheng H. C., Kemp B. E., Pearson R. B., Smith A. J., Misconi L., Van Patten S. M., Walsh D. A. A potent synthetic peptide inhibitor of the cAMP-dependent protein kinase. J Biol Chem. 1986 Jan 25;261(3):989–992. [PubMed] [Google Scholar]
  10. Dostmann W. R., Taylor S. S., Genieser H. G., Jastorff B., Døskeland S. O., Ogreid D. Probing the cyclic nucleotide binding sites of cAMP-dependent protein kinases I and II with analogs of adenosine 3',5'-cyclic phosphorothioates. J Biol Chem. 1990 Jun 25;265(18):10484–10491. [PubMed] [Google Scholar]
  11. Eckstein F., Cassel D., Levkovitz H., Lowe M., Selinger Z. Guanosine 5'-O-(2-thiodiphosphate). An inhibitor of adenylate cyclase stimulation by guanine nucleotides and fluoride ions. J Biol Chem. 1979 Oct 10;254(19):9829–9834. [PubMed] [Google Scholar]
  12. Eliot L. S., Johnston D. Multiple components of calcium current in acutely dissociated dentate gyrus granule neurons. J Neurophysiol. 1994 Aug;72(2):762–777. doi: 10.1152/jn.1994.72.2.762. [DOI] [PubMed] [Google Scholar]
  13. Frey U., Huang Y. Y., Kandel E. R. Effects of cAMP simulate a late stage of LTP in hippocampal CA1 neurons. Science. 1993 Jun 11;260(5114):1661–1664. doi: 10.1126/science.8389057. [DOI] [PubMed] [Google Scholar]
  14. Graham K. K., Mikolich D. J., Fisher A. E., Posner M. R., Dudley M. N. Pharmacologic evaluation of megestrol acetate oral suspension in cachectic AIDS patients. J Acquir Immune Defic Syndr. 1994 Jun;7(6):580–586. [PubMed] [Google Scholar]
  15. Gregory E. J., Cohen S. C., Oines D. W., Mims C. H. Megestrol acetate therapy for advanced breast cancer. J Clin Oncol. 1985 Feb;3(2):155–160. doi: 10.1200/JCO.1985.3.2.155. [DOI] [PubMed] [Google Scholar]
  16. Hamburger A. W., Parnes H., Gordon G. B., Shantz L. M., O'Donnell K. A., Aisner J. Megestrol acetate-induced differentiation of 3T3-L1 adipocytes in vitro. Semin Oncol. 1988 Apr;15(2 Suppl 1):76–78. [PubMed] [Google Scholar]
  17. Hepler J. R., Gilman A. G. G proteins. Trends Biochem Sci. 1992 Oct;17(10):383–387. doi: 10.1016/0968-0004(92)90005-t. [DOI] [PubMed] [Google Scholar]
  18. Hille B. G protein-coupled mechanisms and nervous signaling. Neuron. 1992 Aug;9(2):187–195. doi: 10.1016/0896-6273(92)90158-a. [DOI] [PubMed] [Google Scholar]
  19. House C., Kemp B. E. Protein kinase C contains a pseudosubstrate prototope in its regulatory domain. Science. 1987 Dec 18;238(4834):1726–1728. doi: 10.1126/science.3686012. [DOI] [PubMed] [Google Scholar]
  20. Loprinzi C. L., Goldberg R. M., Burnham N. L. Cancer-associated anorexia and cachexia. Implications for drug therapy. Drugs. 1992 Apr;43(4):499–506. doi: 10.2165/00003495-199243040-00006. [DOI] [PubMed] [Google Scholar]
  21. Loprinzi C. L., Schaid D. J., Dose A. M., Burnham N. L., Jensen M. D. Body-composition changes in patients who gain weight while receiving megestrol acetate. J Clin Oncol. 1993 Jan;11(1):152–154. doi: 10.1200/JCO.1993.11.1.152. [DOI] [PubMed] [Google Scholar]
  22. Mintz I. M., Adams M. E., Bean B. P. P-type calcium channels in rat central and peripheral neurons. Neuron. 1992 Jul;9(1):85–95. doi: 10.1016/0896-6273(92)90223-z. [DOI] [PubMed] [Google Scholar]
  23. Morgan L. R. Megestrol acetate v tamoxifen in advanced breast cancer in postmenopausal patients. Semin Oncol. 1985 Mar;12(1 Suppl 1):43–47. [PubMed] [Google Scholar]
  24. Nelson K. A., Walsh D., Sheehan F. A. The cancer anorexia-cachexia syndrome. J Clin Oncol. 1994 Jan;12(1):213–225. doi: 10.1200/JCO.1994.12.1.213. [DOI] [PubMed] [Google Scholar]
  25. Orr J. W., Keranen L. M., Newton A. C. Reversible exposure of the pseudosubstrate domain of protein kinase C by phosphatidylserine and diacylglycerol. J Biol Chem. 1992 Aug 5;267(22):15263–15266. [PubMed] [Google Scholar]
  26. Plata-Salamán C. R. Regulation of hunger and satiety in man. Dig Dis. 1991;9(5):253–268. doi: 10.1159/000171310. [DOI] [PubMed] [Google Scholar]
  27. Regan L. J., Sah D. W., Bean B. P. Ca2+ channels in rat central and peripheral neurons: high-threshold current resistant to dihydropyridine blockers and omega-conotoxin. Neuron. 1991 Feb;6(2):269–280. doi: 10.1016/0896-6273(91)90362-4. [DOI] [PubMed] [Google Scholar]
  28. Richmond G., Clemens L. Ventromedial hypothalamic lesions and cholinergic control of female sexual behavior. Physiol Behav. 1988;42(2):179–182. doi: 10.1016/0031-9384(88)90295-8. [DOI] [PubMed] [Google Scholar]
  29. Smith S. S., Waterhouse B. D., Woodward D. J. Locally applied progesterone metabolites alter neuronal responsiveness in the cerebellum. Brain Res Bull. 1987 Jun;18(6):739–747. doi: 10.1016/0361-9230(87)90209-7. [DOI] [PubMed] [Google Scholar]
  30. Tisdale M. J. Cancer cachexia. Anticancer Drugs. 1993 Apr;4(2):115–125. doi: 10.1097/00001813-199304000-00001. [DOI] [PubMed] [Google Scholar]
  31. Toullec D., Pianetti P., Coste H., Bellevergue P., Grand-Perret T., Ajakane M., Baudet V., Boissin P., Boursier E., Loriolle F. The bisindolylmaleimide GF 109203X is a potent and selective inhibitor of protein kinase C. J Biol Chem. 1991 Aug 25;266(24):15771–15781. [PubMed] [Google Scholar]
  32. Tsien R. W., Lipscombe D., Madison D. V., Bley K. R., Fox A. P. Multiple types of neuronal calcium channels and their selective modulation. Trends Neurosci. 1988 Oct;11(10):431–438. doi: 10.1016/0166-2236(88)90194-4. [DOI] [PubMed] [Google Scholar]
  33. Umemiya M., Berger A. J. Properties and function of low- and high-voltage-activated Ca2+ channels in hypoglossal motoneurons. J Neurosci. 1994 Sep;14(9):5652–5660. doi: 10.1523/JNEUROSCI.14-09-05652.1994. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Wang H. Y., Watkins D. C., Malbon C. C. Antisense oligodeoxynucleotides to GS protein alpha-subunit sequence accelerate differentiation of fibroblasts to adipocytes. Nature. 1992 Jul 23;358(6384):334–337. doi: 10.1038/358334a0. [DOI] [PubMed] [Google Scholar]
  35. Wu F. S., Gibbs T. T., Farb D. H. Inverse modulation of gamma-aminobutyric acid- and glycine-induced currents by progesterone. Mol Pharmacol. 1990 May;37(5):597–602. [PubMed] [Google Scholar]
  36. Zhu Y., Ikeda S. R. VIP inhibits N-type Ca2+ channels of sympathetic neurons via a pertussis toxin-insensitive but cholera toxin-sensitive pathway. Neuron. 1994 Sep;13(3):657–669. doi: 10.1016/0896-6273(94)90033-7. [DOI] [PubMed] [Google Scholar]
  37. ffrench-Mullen J. M., Danks P., Spence K. T. Neurosteroids modulate calcium currents in hippocampal CA1 neurons via a pertussis toxin-sensitive G-protein-coupled mechanism. J Neurosci. 1994 Apr;14(4):1963–1977. doi: 10.1523/JNEUROSCI.14-04-01963.1994. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. ffrench-Mullen J. M., Plata-Salamán C. R., Buckley N. J., Danks P. Muscarine modulation by a G-protein alpha-subunit of delayed rectifier K+ current in rat ventromedial hypothalamic neurones. J Physiol. 1994 Jan 1;474(1):21–26. doi: 10.1113/jphysiol.1994.sp019998. [DOI] [PMC free article] [PubMed] [Google Scholar]

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