Abstract
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 Ca^2+^ ([Ca^2+^]~i~). This response is biphasic and results from contributions of Ca^2+^ from internal stores, uptake of Ca^2+^ across the plasma membrane and possibly a decrease in Ca^2+^ efflux. These responses have been linked through the activity of inositol 1,4,5‐trisphosphate in releasing Ca^2+^ from internal stores and potentially mediating Ca^2+^ uptakeacross 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 [Ca^2+^]~i~ responses by loading cells with the Ca^2+^ chelator 1,2‐bis(Oaminophenoxy)ethaneN,N,N',N'‐tetraacetate (BAPTA). In BAPTA‐loaded T cells, we have shown that Ca^2+^ mobilized from intracellular stores following activation is effectively buffered, while stimulated Ca^2+^ uptake and associated changes in [Ca^2+^]~i~ were relatively unaffected. In this report, we show that the sustained increase in [Ca^2+^]~i~ is due to increased unidirectional influx of external Ca^2+^ without changes in efflux and that it is the entry of extracellular Ca^2+^ which is sensitive to the transmembrane potential.