Effects of leptin on intracellular calcium concentrations in isolated porcine somatotropes

Neuroendocrinology. 2004;80(2):73-82. doi: 10.1159/000081843. Epub 2004 Nov 2.

Abstract

Leptin, the product of the obese gene, is a protein that is secreted primarily from adipocytes. Leptin can influence the function of the pituitary gland through its action on the hypothalamus, but it can also directly act at the level of the pituitary gland. The ability of leptin to induce an increase in intracellular Ca2+ concentration ([Ca2+]i) in somatotropes was examined in dispersed porcine pituitary cells using a calcium imaging system. Somatotropes were functionally identified by the application of human growth hormone releasing hormone. Leptin increased [Ca2+]i in porcine somatotropes in a dose-dependent manner. The application of 100 nM leptin for 3 min did not have a significant effect on [Ca2+]i, while a 3-min application of 1 microM leptin increased [Ca2+]i in about 50% of the somatotropes (p < 0.01). The application of a second leptin challenge (1 microM) evoked a response in only 18% of the observed somatotropes. The stimulatory effect of leptin was abolished in low calcium saline and blocked by nifedipine, an L-calcium channel blocker, suggesting an involvement of calcium channels. Pretreatment of the cultures with AG 490, a specific Janus kinase inhibitor, and with SB 203580, a mitogen-activated protein kinase (MAP kinase) inhibitor, abolished the increase in [Ca2+]i evoked by leptin. In the presence of N(omega)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, the magnitude of the increase in [Ca2+]i evoked by 1 microM leptin was not significantly changed. However, in the presence of L-NAME only 24% of the somatotropes responded to leptin, while in parallel control cultures 70% of the somatotropes responded to leptin. These results imply an involvement of Janus kinase/signal transducer and activator or transcription, MAP kinase and NOS-signaling pathways in the stimulatory effect of leptin on porcine somatotropes.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Animals, Newborn
  • Calcium / metabolism*
  • Calcium Channel Blockers / pharmacology
  • Calcium Channels / drug effects
  • Calcium Channels / metabolism
  • Cells, Cultured
  • DNA-Binding Proteins / drug effects
  • DNA-Binding Proteins / metabolism
  • In Vitro Techniques
  • Intracellular Fluid / chemistry
  • Leptin / pharmacology*
  • Mitogen-Activated Protein Kinases / drug effects
  • Mitogen-Activated Protein Kinases / metabolism
  • Nifedipine / pharmacology
  • Nitric Oxide Synthase / drug effects
  • Nitric Oxide Synthase / metabolism
  • Pituitary Gland, Anterior / cytology*
  • Pituitary Gland, Anterior / drug effects*
  • Protein-Tyrosine Kinases / drug effects
  • Protein-Tyrosine Kinases / metabolism
  • Signal Transduction / drug effects
  • Signal Transduction / physiology*
  • Swine
  • Trans-Activators / drug effects
  • Trans-Activators / metabolism

Substances

  • Calcium Channel Blockers
  • Calcium Channels
  • DNA-Binding Proteins
  • Leptin
  • Trans-Activators
  • Nitric Oxide Synthase
  • Protein-Tyrosine Kinases
  • Mitogen-Activated Protein Kinases
  • Nifedipine
  • Calcium