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Calcium‐Dependent Transferrin Receptor Recycling in Bovine Chromaffin Cells
Author(s) -
Knight Derek E.
Publication year - 2002
Publication title -
traffic
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.677
H-Index - 130
eISSN - 1600-0854
pISSN - 1398-9219
DOI - 10.1034/j.1600-0854.2002.030407.x
Subject(s) - transferrin , secretion , calcium , biology , endosome , extracellular , transferrin receptor , exocytosis , microbiology and biotechnology , catecholamine , intracellular , vesicle , biochemistry , biophysics , medicine , endocrinology , membrane
The release of regulated secretory granules is known to be calcium dependent. To examine the Ca 2+ ‐dependence of other exocytic fusion events, transferrin recycling in bovine chromaffin cells was examined. Internalised 125 I‐transferrin was released constitutively from cells with a half‐time of about 7 min. Secretagogues that triggered catecholamine secretion doubled the rate of 125 I‐transferrin release, the time courses of the two triggered secretory responses being similar. The triggered 125 I‐transferrin release came from recycling endosomes rather than from sorting endosomes or a triggered secretory vesicle pool. Triggered 125 I‐transferrin release, like catecholamine secretion from the same cells, was calcium dependent but the affinities for calcium were very different. The extracellular calcium concentrations that gave rise to half‐maximal evoked secretion were 0.1 m m for 125 I‐transferrin and 1.0 m m for catecholamine, and the intracellular concentrations were 0.1 μ m and 1 μ m , respectively. There was significant 125 I‐transferrin recycling in the virtual absence of intracellular Ca 2+ , but the rate increased when Ca 2+ was raised above 1 n m , and peaked at 1 μ m when the rate had doubled. Botulinum toxin type D blocked both transferrin recycling and catecholamine secretion. These results indicate that a major component of the vesicular transport required for the constitutive recycling of transferrin in quiescent cells is calcium dependent and thus under physiological control, and also that some of the molecular machinery involved in transferrin recycling/fusion processes is shared with that for triggered neurosecretion.