- GTP signaling
GTP is a chemorepellent in Tetrahymena thermophila, causing cells to exhibit avoidance behavior, characterized by ciliary reversal. Recent work in our laboratory has shown that tyrosine kinase activity is required in order for GTP signaling to take place (Bartholomew et al., submitted for publication). Second messengers which we have found to be important for GTP signaling in Tetrahymena include nitric oxide and cGMP. Previous studies by Kim et al., 1999, have shown that a calcium-based depolarization is elicited by the application of extracellular GTP. Currently, our lab is addressing the question of where intracellular calcium is involved in the GTP chemoresponse. Addition of the membrane-permeable calcium chelator, BAPTA-AM, to the extracellular medium abolishes the GTP chemoresponse in Tetrahymena. However, addition of this chelator to the extracellular medium does not affect the level of GTP-induced tyrosine phosphorylation, as detected by indirect immunofluorescence. As we continue to pursue the question of where calcium is involved in GTP signaling, we will look at calcium involvement in the nitric oxide/cGMP pathway.