Ammonium ions mobilize calcium from an internal pool which is insensitive to TRH and ionomycin in bovine anterior pituitary cells

Cell Calcium. 1991 Apr;12(4):301-12. doi: 10.1016/0143-4160(91)90004-x.

Abstract

The effects of NH4Cl on cytoplasmic free calcium concentration ([Ca2+]i) and pH (pHi) in single bovine anterior pituitary cells were determined using fluorescence imaging microscopy. Addition of NH4Cl (10-40 mM) in the presence of 1 mM extracellular calcium ([Ca2+]e) increased [Ca2+]i to a peak which then fell to a sustained plateau, returning to resting levels upon removal of NH4Cl. In medium containing 0.1 microM [Ca2+]e, or in 1 mM [Ca2+]e medium containing 0.1 microM nitrendipine, the plateau was absent leaving only a transient [Ca2+]i spike. NH4Cl also increased pHi and this, like the [Ca2+]i plateau, remained elevated during the continued presence of NH4Cl. In medium containing only 0.1 microM [Ca2+]e, to preclude refilling of internal stores by entry of external calcium, repeated exposures to NH4Cl induced repeated [Ca2+]i transients. In contrast, only the initial exposure to thyrotropin releasing hormone (TRH; 20-500 nM) caused a [Ca2+]i rise but, after an additional exposure to NH4CI, TRH responses re-emerged in some cells. Pre-treatment with the calcium ionophore ionomycin abolished the rise caused by TRH, but neither TRH nor ionomycin pretreatment affected the response to NH4Cl. Neither acetate removal nor methylamine increased [Ca2+]i in medium containing 0.1 microM [Ca2+]e, although in both cases pHi increased. We conclude that in bovine anterior pituitary cells NH4Cl raises [Ca2+]i by two independent pathways, increasing net calcium entry and mobilizing Ca2+ from a TRH-insensitive calcium store.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ammonium Chloride / pharmacology*
  • Animals
  • Calcium / analysis
  • Calcium / metabolism*
  • Cattle
  • Cells, Cultured
  • Cytoplasm / metabolism
  • Fura-2
  • Hydrogen-Ion Concentration
  • Ionomycin / pharmacology*
  • Microscopy, Fluorescence
  • Pituitary Gland, Anterior / drug effects
  • Pituitary Gland, Anterior / metabolism*
  • Serum Albumin, Bovine
  • Thyrotropin-Releasing Hormone / analysis
  • Thyrotropin-Releasing Hormone / metabolism
  • Thyrotropin-Releasing Hormone / pharmacology*

Substances

  • Ammonium Chloride
  • Serum Albumin, Bovine
  • Ionomycin
  • Thyrotropin-Releasing Hormone
  • Calcium
  • Fura-2