Control of Ca2+ channel current and exocytosis in rat lactotrophs by basally active protein kinase C and calcineurin

Alla F Fomina, E. S. Levitan

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

Modulation of voltage-activated Ca2+ channel activity by phosphorylation was studied in metabolically intact voltage-clamped rat lactotrophs. Experiments using Ba2+ as a charge carrier indicated that a phorbol ester protein kinase C activator stimulates high-voltage-activated Ca2+ channel currents, but has no effect on low-voltage-activated currents. Extracellular application of structurally and mechanistically distinct protein kinase C inhibitors (staurosporin, H7, calphostin C, chelerythrine and Ro 31-8220) preferentially inhibited the high-voltage-activated Ba2+ current. This suggests that protein kinase C is required for maintainance of Ca2+ channel activity even in the absence of modulators. Cyclosporin A, an inhibitor of the Ca2+/calmodulin-dependent protein phosphatase calcineurin, increased the high-voltage-activated Ca2+ channel current, and staurosporin reversed this effect. Thus, dephosphosphorylation by calcineurin may limit basal Ca2+ channel activity. Time-domain monitoring of cellular capacitance changes demonstrated that cyclosporin A and 12-O-tetradecanoyl-phorbol-13-acetate do not affect exocytosis at a hyperpolarized potential, but each enhances depolarization-induced exocytosis. Facilitation of exocytosis by cyclosporin A differed from 12-O-tetradecanoyl-phorbol-13-acetate in that it was biphasic. The delayed facilitation induced by cyclosporin A could be accounted for by stimulation of the voltage-gated Ca2+ current. These results suggest that the high-voltage activated Ca2+ channel current in rat lactotrophs is determined by the opposing basal activities of protein kinase C and calcineurin. Furthermore, it is concluded that the regulation of Ca2+ channels by protein kinase C and calcineurin affects depolarization-induced exocytosis.

Original languageEnglish (US)
Pages (from-to)523-531
Number of pages9
JournalNeuroscience
Volume78
Issue number2
DOIs
StatePublished - Mar 10 1997
Externally publishedYes

Fingerprint

Lactotrophs
Calcineurin
Exocytosis
Protein Kinase C
Cyclosporine
Tetradecanoylphorbol Acetate
Protein C Inhibitor
Phosphoprotein Phosphatases
Phorbol Esters
Calmodulin
Protein Kinase Inhibitors
Phosphorylation

Keywords

  • calcium channel
  • phosphatase
  • pituitary
  • prolactin
  • protein kinase
  • secretion

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Control of Ca2+ channel current and exocytosis in rat lactotrophs by basally active protein kinase C and calcineurin. / Fomina, Alla F; Levitan, E. S.

In: Neuroscience, Vol. 78, No. 2, 10.03.1997, p. 523-531.

Research output: Contribution to journalArticle

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