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

• Published in: Neuron (Cambridge, Mass.) Vol. 11; no. 1; pp. 93 - 104
• Main Authors: THOMAS, P, WONG, J. G, LEE, A. K, ALMERS, W
• Format: Journal Article
• Language: English
• Published: Cambridge, MA Cell Press 01.07.1993
• Subjects: Acetates - pharmacology; Adenosine Triphosphate - physiology; Binding, Competitive; Biological and medical sciences; Calcium - metabolism; Chelating Agents - pharmacology; Cytosol - metabolism; Ethylenediamines - pharmacology; Exocytosis - physiology; Fundamental and applied biological sciences. Psychology; Hormones and neuropeptides. Regulation; Hydrogen-Ion Concentration; Hypothalamus. Hypophysis. Epiphysis. Urophysis; 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; Vertebrates: endocrinology; Vertebrata; Regulation(control); Endocrine gland; Mammalia; Calcium; Rat; Rodentia; Pituitary gland; Intracellular; Exocytosis; Melanotropic cell; Endocrine secretion
• ISSN: 0896-6273; 1097-4199
• DOI: 10.1016/0896-6273(93)90274-U

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.