Figure 4.

Functional expression of Trp proteins enhances CCE in COS Cells. (A) Enhancement of agonist-stimulated CCE by expression of hTrp3 in COS cells. Note that expression of the Trp protein caused an enhancement of CCE [adapted from Zhu et al. (6)]. (B) Rapid activation of mTrp6-induced Ca²⁺ influx occurs within the same time frame as IP3-induced Ca²⁺ release. Note that while, in the absence of external Ca²⁺, the initial IP3-mediated increase in [Ca²⁺]_i in mTrp6-expressing cells is not significantly different from that seen in cells expressing the M5 receptor alone, the presence of external Ca²⁺ uncovers rapid stimulation of an additional flux of Ca²⁺ into the cytoplasm, which we interpret to come from the extracellular space and entering through CCE channels formed of Trp subunits. (C) Trp-based CCE channels are stimulated by store depletion. The figure shows agonist-independent activation of CCE by thapsigargin-induced depletion of Ca²⁺ stores in COS cells and its enhancement by either wild-type hTrp3.