In this report, we describe a Jurkat cell variant, termed JCT8, the selection of which is based upon its resistance to cell-growth inhibition mediated by the holotoxin of Vibrio cholerae, cholera toxin (CT). JCT8 cells exhibit normal cAMP production in response to various cAMP inducers, including CT, together with conserved ADP ribosylation in vitro of G-protein Gsα by the A subunit of the toxin. However, after a 4-h pretreatment with CT, JCT8 cells have a conserved expression of cell-surface CD3 molecules. These effects are in contrast to those elicited by the toxin in long term PGE₂-desensitized Jurkat cells, which remain as sensitive as the wild type to the inhibitory action of CT on cell growth and CD3 cell-surface expression, despite poor responsiveness to CT with regard to cAMP production. In JCT8 cells, Ca²⁺ mobilization induced via the CD3/TCR is maintained after CT treatment contrasting with its complete suppression in the wild-type and in the PGE₂-desensitized cells. However, as in the other cell types, CT still suppresses Ca²⁺ influx in JCT8 cells. Increase in inositol phosphates by CD3 stimulation of JCT8 cells, including of inositol 1.4,5-triphosphate (I(1,4,5)P₃), is only partially antagonized by CT. This suggests either that in JCT8 cells there is a different susceptibility of Ca²⁺ mobilization and influx to partial inhibition by CT of CDS-triggered phospholipase C (PLC)-induced phosphoinositide hydrolysis or that an additional and PLC-independent suppressive effect of the toxin on Ca²⁺ influx may exist. To investigate this particular point further, we use Thapsigargin, a Ca²⁺-endoplasmic reticulum ATPase inhibitor that can mobilize in human T lymphocytes I(1,4,5)P₃-dependent intracellular Ca²⁺ pools by a PLC-independent pathway. We demonstrate that the Ca²⁺ influx triggered in the wild-type Jurkat cells or in JCT8 cells by Thapsigargin is antagonized by CT. The present data are therefore consistent with the idea that CT specifically impairs in the Jurkat T cell model the entry of Ca²⁺ from extracellular spaces by a mechanism independent not only from cAMP but also in part from inhibition by the toxin of phosphoinositide hydrolysis.