Taste Cells of the Type III Employ CASR to Maintain Steady Serotonin Exocytosis at Variable Ca2+ in the Extracellular Medium

Cells. 2022 Apr 18;11(8):1369. doi: 10.3390/cells11081369.


Type III taste cells are the only taste bud cells which express voltage-gated (VG) Ca2+ channels and employ Ca2+-dependent exocytosis to release neurotransmitters, particularly serotonin. The taste bud is a tightly packed cell population, wherein extracellular Ca2+ is expected to fluctuate markedly due to the electrical activity of taste cells. It is currently unclear whether the Ca2+ entry-driven synapse in type III cells could be reliable enough at unsteady extracellular Ca2. Here we assayed depolarization-induced Ca2+ signals and associated serotonin release in isolated type III cells at varied extracellular Ca2+. It turned out that the same depolarizing stimulus elicited invariant Ca2+ signals in type III cells irrespective of bath Ca2+ varied within 0.5-5 mM. The serotonin release from type III cells was assayed with the biosensor approach by using HEK-293 cells co-expressing the recombinant 5-HT4 receptor and genetically encoded cAMP sensor Pink Flamindo. Consistently with the weak Ca2+ dependence of intracellular Ca2+ transients produced by VG Ca2+ entry, depolarization-triggered serotonin secretion varied negligibly with bath Ca2+. The evidence implicated the extracellular Ca2+-sensing receptor in mediating the negative feedback mechanism that regulates VG Ca2+ entry and levels off serotonin release in type III cells at deviating Ca2+ in the extracellular medium.

Keywords: extracellular Ca2+-sensing receptor; serotonin biosensor; serotonin secretion; taste cells; voltage-gated Ca2+ channels.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calcium / metabolism
  • Exocytosis
  • HEK293 Cells
  • Humans
  • Receptors, Calcium-Sensing
  • Serotonin*
  • Taste*


  • CASR protein, human
  • Receptors, Calcium-Sensing
  • Serotonin
  • Calcium