Dissociation of unidirectional influx of external Ca2+ and release from internal stores in activated human T lymphocytes.
Addition of lectin or antibody to the T cell receptor complex of human T cells results in a rapid increase in the concentration of cytoplasmic free Ca2+ ([Ca2+]i). This response is biphasic and results from contributions of Ca2+ from internal stores, uptake of Ca2+ across the plasma membrane and possibly a decrease in Ca2+ efflux. These responses have been linked through the activity of inositol 1,4,5-trisphosphate in releasing Ca2+ from internal stores and potentially mediating Ca2+ uptake across the plasma membrane. Following addition of phytohemagglutinin or anti-CD3 antibody to resting T cells or Jurkat cells, we have been able to dissociate the [Ca2+]i responses by loading cells with the Ca2+ chelator 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetate (BAPTA). In BAPTA-loaded T cells, we have shown that Ca2+ mobilized from intracellular stores following activation is effectively buffered, while stimulated Ca2+ uptake and associated changes in [Ca2+]i were relatively unaffected. In this report, we show that the sustained increase in [Ca2+]i is due to increased unidirectional influx of external Ca2+ without changes in efflux and that it is the entry of extracellular Ca2+ which is sensitive to the transmembrane potential.
Gelfand
E W
EW
Department of Pediatrics, National Jewish Center for Immunology and Respiratory Medicine, Denver, CO 80206.
Cheung
R K
RK
D002118:Calcium / Q000097:blood*; D002614:Chelating Agents / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D008213:Lymphocyte Activation / Q000502:physiology*; D008345:Manganese / Q000097:blood; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*
D002614:Chelating Agents; D008345:Manganese; D002118:Calcium