Voltage-dependent potassium currents in ovine somatotrophs and their function in growth hormone secretion

C. Chen, P. Heyward, J. Zhang, D. Wu, I. J. Clarke

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Abstract

Sheep somatotroph-enriched cultures were obtained by means of enzyme dissociation and Percoll gradient separation. Nystatin-perforated-whole-cell recordings were performed on post-recording-identified somatotrophs after 4-14 days in vitro. Using Ca2+-free, tetrodotoxin-containing (1 μM) bath solution and K+ electrode solution, three types of voltage-dependent K+ currents were recorded as inward rectifying, outward transient and outward delayed rectifying K+ currents. The inward rectifying K+ current was very small at physiological extracellular K+ concentrations (5 mM) and enhanced by increasing the K+ concentration in the bath to 55 mM; it was blocked by tetraethylammonium (2 mM) but not by 4-aminopyridine (5 mM). A transient outward K+ current appeared at -50 mV and was selectively diminished by 4-aminopyridine (2 or 4 mM). A delayed rectifying outward K+ current was observed when the membrane potential was depolarized to -20 mV and was blocked by tetraethylammonium (2 mM) but not 4-aminopyridine (4 mM). Application of 4-aminopyridine but not tetraethylammonium (up to 5 mM) depolarized the cell membrane potential recorded under current clamp conditions and triggered action potentials when the bath solution contained Ca2+ (2 mM) but not tetrodotoxin. The intracellular Ca2+ concentration was increased by 4-aminopyridine as was growth hormone release. Therefore, the 4-aminopyridine-sensitive transient outward K+ current appears to be important in the determining the resting potential of ovine somatotrophs and plays a major role in regulating basal intracellular Ca2+ concentration and growth hormone secretion.

Original languageEnglish
Pages (from-to)1-9
Number of pages9
JournalNeuroendocrinology
Volume59
Issue number1
DOIs
Publication statusPublished - 1 Jan 1994
Externally publishedYes

Keywords

  • Ca
  • Growth hormone
  • K currents
  • Patch clamp
  • Somatotrophs

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