Diacylglycerol modulates action potential frequency in GH3 pituitary cells: correlative biochemical and electrophysiological studies

Charles M. Gammon, Gerry S. Oxford, Ann C. Allen, Ken D. McCarthy, Pierre Morell

Research output: Contribution to journalArticle

20 Scopus citations

Abstract

We have investigated the involvement of enhanced phosphoinositide metabolism in mediating TRH-induced alteration of electrophysiological events related to prolactin secretion by GH3 cells (a line of pituitary origin). Patch-clamp recording (in the current clamp, whole-cell configuration) showed that a few seconds after TRH application there was a brief period (about 30 s) of membrane hyperpolarization followed by several minutes of increased calcium-dependent action potential frequency. In parallel experiments cells were labeled for 24 h with either [3H]myo-inositol or [3H]arachidonate. Application of TRH resulted in rapid increases in levels of inositol phosphates and diacylglycerol. The time course of elevation of inositol 1,4,5-triphosphate (maximal by 5 s) is compatible with an initial burst of intracellular calcium mobilization associated with a transient phase of TRH-induced prolactin release. Application of TRH was also followed by a rapid but more sustained (several minutes) period of elevated diglyceride accumulation; a time course corresponding to a prolonged period of prolactin release which is dependent on the influx of external calcium. A causal relationship between diglyceride release and increased action potential frequency was demonstrated since local application (via a U-tube apparatus) of either 2 μM phorbol ester (phorbol 12,13-dibutyrate or phorbol 12-myristate 13-acetate) or 60 μM 1-oleoyl-2-acetyl-glycerol to patch-clamped cells could mimic this aspect of the TRH effect. In contrast, the inactive phorbol ester, 4α-phorbol, was unable to elicit this response. We suggest that the second (prolonged) phase of TRH-stimulated prolactin release involves phospholipase C-catalyzed formation of diglyceride with a resulting protein kinase C-mediated alteration of ion channel properties. These changes in channel properties lead to increased action potential frequency and a consequent influx of extracellular calcium.

Original languageEnglish (US)
Pages (from-to)217-224
Number of pages8
JournalBrain research
Volume479
Issue number2
DOIs
StatePublished - Feb 13 1989

Keywords

  • Action potential frequency
  • Diacylglycerol
  • GH cell
  • Inositol phosphate
  • Phorbol ester
  • Thyrotropin-releasing hormone

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology

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