Immunogold-labeled transmission electron microscopy (TEM) was used to determine the total number of secretory vesicles in resting and in growth hormone (GH)-stimulated porcine pituitary cells. We identified three categories of vesicles: filled, empty, and partly empty. Resting GH cells contained more than twice as many filled vesicles than did the stimulated ones. Stimulated cells, however, contained nearly twice as many empty vesicles and 2.5 times more partly empty vesicles than did resting cells. Secretory vesicles in GH cells further revealed the localization of GH only in electron-dense vesicles in both resting and stimulated cells. The total number of secretory vesicles did not change after secretion. These results are consistent with a mechanism that, after stimulation of secretion, vesicles transiently dock and fuse at the fusion pore to release vesicular contents.
LawsonD, FewtrellC, GompertsB, RaffMC. Anti-immunoglobulin-induced histamine secretion by rat peritoneal mast cells studied by immunoferritin electron microscopy. J Exp Med142: 391–401, 1975.
2.
PlattnerH, ArtalejoAR, NeherE. Ultrastructural organization of bovine chromaffin cell cortex-analysis by cryofixation and morphometry of aspects pertinent to exocytosis. J Cell Biol139: 1709–1717, 1997.
3.
SchneiderSW, SritharanKC, GeibelJP, OberleithnerH, JenaBP. Surface dynamics in living acinar cells imaged by atomic force microscopy: identification of plasma membrane structures involved in exocytosis. Proc Natl Acad Sci U S A94: 316–321, 1997.
4.
ChoS-J, KellyM, RognlienKT, ChoJ, HorberJK, JenaBP. SNAREs in opposing bilayers interact in a circular array to form conducting pores. Biophys J83: 2522–2527, 2002.
5.
ChoS-J, QuinnAS, StromerMH, DashS, ChoJ, TaatjesDJ, JenaBP. Structure and dynamics of the fusion pore in live cells. Cell Biol Int26: 35–42, 2002.
6.
ChoS-J, JeftinijaK, GlavaskiA, JeftinijaS, JenaBP, AndersonLL. Structure and dynamics of the fusion pores in live GH-secreting cells revealed using atomic force microscopy. Endocrinology143: 1144–1148, 2002.
7.
ChoS-J, WakadeA, PappasGD, JenaBP. New structure involved in transient membrane fusion and exocytosis. Ann N Y Acad Sci971: 254–256, 2002.
8.
JenaBP, ChoS-J, JeremicA, StromerMH, Abu-HamdahR. Structure and composition of the fusion pore. Biophys J84: 1337–1343, 2003.
ChoS-J, ChoJ, JenaBP. The number of secretory vesicles remains unchanged following exocytosis. Cell Biol Int26: 29–33, 2002.
11.
JenaBP. Fusion pore in live cells. News Physiol Sci17: 219–222, 2002.
12.
ReyoldsES. The use of lead citrate at high pH as an electron-opaque stain in electron microscopy. J Cell Biol17: 208–212, 1963.
13.
Glavaski-JoksimovicA, JeftinijaK, JeremicA, AndersonLL, JeftinijaS. Mechanism of action of the growth hormone secretagogue, L-692,585, on isolated porcine somatotropes. J Endocrinol175: 625–636, 2002.
14.
Glavaski-JoksimovicA, JeftinijaK, ScanesCG, AndersonLL, JeftinijaS. Stimulatory effect of ghrelin on isolated porcine somatotropes. Neuroendocrinology77: 366–378, 2003.
15.
BreckenridgeU, AlmersW. Final steps in exocytosis observed in a cell with giant secretory granules. Proc Natl Acad Sci U S A84: 1945–1949, 1987.
16.
BreckenridgeLJ, AlmersW. Currents through the fusion pore that forms during exocytosis of a secretory vesicle. Nature328: 814–817, 1987.
17.
ValentijnK, ValentijnJA, JamiesonJD. Role of actin in regulated exocytosis and compensatory membrane retrieval: insights from an old acquaintance. Biochem Biophys Res Commun266: 652–661, 1999.
18.
TaraskaJW, PerraisD, Ohara-ImaizumiM, NagamatsuS, AlmersW. Secretory granules are recaptured largely intact after stimulated exocytosis in cultured endocrine cells. Proc Natl Acad Sci U S A100: 2070–2075, 2003.
19.
AravanisAM, PyleJS, TsienRW. Single synaptic vesicles fusing transiently and successively without loss of identity. Nature423: 643–647, 2003.
20.
AndersonLL. Discovery of a new cellular structure—the Porosome: elucidation of the molecular mechanism of secretion. Cell Biol Int28: 3–5, 2004.
21.
JeremicA, KellyM, ChoJ-A, ChoS-J, Heinrich HoberJK, JenaBP. Calcium drives fusion of SNARE-apposed bilayers. Cell Biol Int28: 19–31, 2004.
22.
KilicG, AnglesonJK, CochillaAJ, NussinovitchI, BetzWJ. Sustained stimulation of exocytosis triggers continuous membrane retrieval in rat pituitary somatotrophs. J Physiol532: 771–783, 2001.
23.
MajóG, AguadoF, BlasiJ, MarsalJ. Synaptobrevin isoforms in secretory granules and synaptic-like microvesicles in anterior pituitary cells. Life Sci62: 607–616, 1998.
24.
LeeJ-S, MayesMS, StromerMH, JeftinijaK, JeftinijaS, JenaBP., AndersonLL. Immunocytochemical study of spatial distribution pattern and number of secretory vesicles of somatotrophs in porcine anterior pituitary. In: LambertsSWJ, MelmedS, Eds., Proceedings of the 8th International Pituitary Congress, June 22–25, 2003. Dordrecht, The Netherlands: Kluwer Academic, pp 55, 2003.
25.
ChoSJ, SattarAK, JeongEH, SatchiM, ChoJA, DashS. Aquaporin 1 regulates GTP-induced rapid gating of water in secretory vesicles. Proc Natl Acad Sci U S A99: 4720–2724, 2002.
26.
Abu-HamdahR, ChoWJ, ChoSJ, JeremicA, KellyM, HieAE, JenaBP. Regulation of the water channel aquaporin-1: isolation and reconstitution of the regulatory complex. Cell Biol Int28: 7–17, 2004.
27.
JenaBP. Exocytotic fusion: total or transient?Cell Biol Int21: 257–259, 1997.
28.
JenaBP. Fusion pores: structure and dynamics. J Endocrinol176: 169–174, 2003.
29.
JenaBP, SchneiderSW, GeibelJP, WebsterP, OberleithnerH, SritharanKC. Gi regulation of secretory vesicle swelling examined by atomic force microscopy. Proc Natl Acad Sci U S A94: 13317–13322, 1997.
30.
JeongEH, WebsterP, KhuongCQ, SattarAK, SatchiM, JenaBP. The native membrane fusion machinery in cells. Cell Biol Int22: 657–670, 1998.
31.
HickeyGJ, DriskoJ, FaidleyT, ChangC, AndersonLL, NicolichS, McGuireL, RickesE, KrupaD, FeeneyW, FriscinoB, CunninghamP. Frazier E, Chen H, Laroque P, Smith RG. Mediation by the central nervous system is critical to the in vivo activity of the GH secretagogue L-692,585. J Endocrinol148: 371–380, 1996.
32.
KlindtJ, StoneRT. Porcine growth hormone and prolactin secretion: concentration in the fetus and secretory patterns on the growing pig. Growth48: 1–15, 1984.
33.
KlindtJ. Porcine growth hormone and prolactin secretion: the first month of postnatal life. Growth50: 516–525, 1986.
34.
ScanesCG, LazarusD, BowenS, BuonomoFC, GilbreathRL. Postnatal changes in circulating concentrations of growth hormone, somatomedin C and thyroid hormones in pigs. Dornest Anim Endocrinol4: 253–257, 1987.
35.
BuonomoFC, KlindtJ. Ontogeny of growth hormone (GH), insulin-like growth factors (IGF-I and IGF-II) and IGF binding protein-2 (IGFBP-2) in genetically lean and obese swine. Dornest Anim Endocrinol10: 257–265, 1993.
36.
SunHS, AndersonLL, YuT-P, KimK-S, KlindtJ, TuggleCK. Neonatal Meishan pigs show POU1F1 genotype effects on plasma GH and PRL concentration. Anim Reprod Sci69: 223–237, 2002.
