A low affinity Ca2+ receptor controls the final steps in peptide secretion from pituitary melanotrophs

Neuron. 1993 Jul;11(1):93-104. doi: 10.1016/0896-6273(93)90274-u.

Abstract

Using flash photolysis of caged Ca2+ and the membrane capacitance to monitor exocytosis, we have studied the response of single melanotrophs to a step rise in cytosolic Ca2+ concentration ([Ca2+]i). Exocytosis begins with a rapid burst. This burst is followed by a slower phase, which is inhibited at cytosolic pH 6.2, and an ultraslow phase, which is strongly temperature sensitive. The exocytic burst starts with a delay of 6-11 ms and continues at a rate that grows steeply with [Ca2+]i and is half-maximal at [Ca2+]i = 27 microM. At least 3 Ca2+ ions are required to trigger exocytosis. The rate constant at saturating [Ca2+]i suggests that exocytosis of a dense core vesicle takes 40 ms after all Ca2+ ions have bound to their regulatory sites. If docked dense core vesicles cause the exocytic burst, they must decorate the plasma membrane at a mean density of 0.5/micron2.

Publication types

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

MeSH terms

  • Acetates / pharmacology
  • Adenosine Triphosphate / physiology
  • Binding, Competitive
  • Calcium / metabolism*
  • Chelating Agents / pharmacology
  • Cytosol / metabolism
  • Ethylenediamines / pharmacology
  • Exocytosis / physiology
  • Hydrogen-Ion Concentration
  • Intracellular Membranes / metabolism
  • Melanocyte-Stimulating Hormones / metabolism*
  • Osmolar Concentration
  • Peptides / metabolism*
  • Pituitary Gland / cytology
  • Pituitary Gland / metabolism*
  • Receptors, Cell Surface / metabolism
  • Receptors, Cell Surface / physiology*
  • Temperature
  • Time Factors

Substances

  • Acetates
  • Chelating Agents
  • Ethylenediamines
  • Peptides
  • Receptors, Cell Surface
  • DM-nitrophen
  • Adenosine Triphosphate
  • Melanocyte-Stimulating Hormones
  • Calcium