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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]
Summary
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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