CALMODULIN REGULATION OF CA2-CELLS( ENTRY IN JURKAT T)

We have previously proposed a role for calmodulin (CaM) in the regulat ion of initiation of Ca2+ entry in Jurkat T cells, as well as in the r egulation of the current that mediates Ca2+ entry, I-T. In this report , we provide evidence for the mechanism of CaM action. We have previou sly shown that activation-induced Ca2+ entry into Jurkat T cells is me diated by a current we have called I-T. In the whole cell variation, b ut not the perforated patch variation, of the patch clamp technique, t his current is short-lived (under 6 min) suggesting that the current i s under the control of a diffusible component of the cytosol. Addition of CaM to the whole cell recording pipette solution maintained I-T fo r up to 20 min, suggesting that CaM may be this diffusible component. Pharmacological inhibitors of CaM blocked the augmentation of I-T norm ally induced by an activating stimulus. Cells electroporated in the pr esence of anti-CaM antibodies had reduced influx of extracellular Ca2, with no change in release of Ca2+ from the internal stores. These ob servations suggest that T cell receptor engagement initiates Ca2+ infl ux by a pathway that likely includes CaM, which may in turn regulate I -T. Influx of extracellular Ca2+ is required for cellular proliferatio n, and inhibition of CaM by pharmacological inhibitors reduced cellula r proliferation. This same inhibition of proliferation was seen in cel ls electroporated with anti-CaM antibodies. This suggests that inhibit ion of CaM and/or I-T may be a target for therapeutic inhibition of in appropriate T cell proliferation.