Abstract

We investigated the organization of spontaneous rises in cytosolic free Ca2+ concentration ([Ca2+]i) due to electrical activity in acute pituitary slices. Real time confocal imaging revealed that 73% of the cells generated fast peaking spontaneous [Ca2+]i transients. Strikingly, groups of apposing cells enhanced their [Ca2+]i in synchrony with a speed of coactivation >1,000 microm/s. Single-cell injection of Neurobiotin or Lucifer yellow labeled clusters of cells, which corresponded to coactive cells. Halothane, a gap junction blocker, markedly reduced the spread of tracers. Coupling between excitable cells was mainly homologous in nature, with a prevalence of growth hormone-containing cells. We conclude that spontaneously active endocrine cells are either single units or arranged in synchronized gap junction-coupled assemblies scattered throughout the anterior pituitary gland. Synchrony between spontaneously excitable cells may help shape the patterns of basal secretion.

Highlights

  • Endocrine pituitary cells that release hormones from large dense core vesicles (LDCV)1 by calcium-mediated exocytosis exhibit spontaneous firing of action potentials

  • Electrical activity has already been detected in the anterior pituitary gland, both in vivo and in tissue preparations [7,8,9], the dynamics and organization of [Ca2ϩ]i rises associated with spontaneous action potentials have not yet been investigated at the tissue level

  • Prevalence of Homologous Coupling between growth hormone (GH)-containing Coactive Cells—Earlier studies carried out in pituitary cells isolated from the tissue have revealed that spontaneous electrical activity and ensuing [Ca2ϩ]i transients were mainly observed in cells containing either GH or prolactin [35]

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Summary

Introduction

Endocrine pituitary cells that release hormones from large dense core vesicles (LDCV)1 by calcium-mediated exocytosis exhibit spontaneous firing of action potentials. By visualizing the multicellular profiles of [Ca2ϩ]i activity in these slices, we detected clusters of spontaneously coactive endocrine cells, which were scattered throughout the anterior pituitary.

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