ATP-dependent uptake of 5-hydroxytryptamine by secretory granules isolated from thyroid parafollicular cells.
The current study was done to test the hypotheses that parafollicular granules contain a vacuolar ATPase (V-ATPase) similar to that found in chromaffin granules, that the transport of H+ into granules mediated by this enzyme drives the granular uptake of 5-hydroxytryptamine (5-HT, serotonin), and that secretagogues stimulate both the acidification of parafollicular granules and their ability to take up 5-HT by opening an anion channel in the granular membrane. Our studies indicate that parafollicular granules contain a V-ATPase that is antigenically similar to that of the V-ATPase of adrenal chromaffin granules; however, the parafollicular granular membrane differs from that of chromaffin granules in permeability to Cl- and K+. The membranes of granules derived from resting parafollicular cells appear to be relatively impermeable to Cl- but permeable to K+. Parafollicular granules (and ghosts derived from them) manifest ATP-dependent transmembrane transport of 5-HT. This transport is more dependent on the pH difference (delta pH) than on the membrane potential component of the proton electrochemical gradient across the granular membrane. Transport of 5-HT is thus inhibited more by exposure of parafollicular granules to agents, such as nigericin, that collapse delta pH than by those, such as valinomycin, that decrease transmembrane difference in potential. ATP-dependent uptake of 5-HT by granules isolated from secretagogue-stimulated parafollicular cells is greater than that into granules isolated from unstimulated cells. Since secretagogues open a Cl- channel in parafollicular granule membranes, which enhances acidification of the granules, the facilitation of 5-HT uptake by secretagogues is probably due to an increase in delta pH.
Cidon
S
S
Department of Anatomy and Cell Biology, Columbia University College of Physicians and Surgeons, New York, New York.
Tamir
H
H
Nunez
E A
EA
Gershon
M D
MD
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active; D015153:Blotting, Western; D003594:Cytoplasmic Granules / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007124:Immunoenzyme Techniques; D066298:In Vitro Techniques; D008564:Membrane Potentials; D011188:Potassium / Q000494:pharmacology; D006180:Proton-Translocating ATPases / Q000145:classification / Q000378:metabolism*; D012110:Reserpine / Q000494:pharmacology; D012701:Serotonin / Q000378:metabolism*; D012756:Sheep; D013961:Thyroid Gland / Q000378:metabolism* / Q000648:ultrastructure; D014634:Valinomycin / Q000494:pharmacology
D014634:Valinomycin; D012701:Serotonin; D012110:Reserpine; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases; D011188:Potassium