Exocytotic insertion of calcium channels constrains compensatory endocytosis to sites of exocytosis.
Proteins inserted into the cell surface by exocytosis are thought to be retrieved by compensatory endocytosis, suggesting that retrieval requires granule proteins. In sea urchin eggs, calcium influx through P-type calcium channels is required for retrieval, and the large size of sea urchin secretory granules permits the direct observation of retrieval. Here we demonstrate that retrieval is limited to sites of prior exocytosis. We tested whether channel distribution can account for the localization of retrieval at exocytotic sites. We find that P-channels reside on secretory granules before fertilization, and are translocated to the egg surface by exocytosis. Our study provides strong evidence that the transitory insertion of P-type calcium channels in the surface membrane plays an obligatory role in the mechanism coupling exocytosis and compensatory endocytosis.
Smith
R M
RM
Medical College of Georgia, Augusta, Georgia 30912-2630, USA.
Baibakov
B
B
Ikebuchi
Y
Y
White
B H
BH
Lambert
N A
NA
Kaczmarek
L K
LK
Vogel
S S
SS
D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002104:Cadmium / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000378:metabolism / Q000494:pharmacology; D020865:Calcium Channels, P-Type / Q000032:analysis / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D003208:Concanavalin A / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D004705:Endocytosis / Q000187:drug effects; D005089:Exocytosis / Q000187:drug effects; D005306:Fertilization / Q000502:physiology; D005456:Fluorescent Dyes / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008854:Microscopy, Electron; D010063:Ovum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D012617:Sea Urchins
D002121:Calcium Channel Blockers; D020865:Calcium Channels, P-Type; D005456:Fluorescent Dyes; D002104:Cadmium; D003208:Concanavalin A; D000001:Calcimycin; D002118:Calcium