FIGURE 6.

Involvement of G_i protein in MCT-1 signaling. Inhibitory effects of PTX on the stimulation with fMLF, MCT-1, and hMCT-1 (A–C) are shown. A, β-hexosaminidase release from cells treated with 50 ng/ml PTX for 16 h (closed symbols) or from control cells (open symbols) after stimulation with various concentration of fMLF (left, circles) or MCT-1 (right, squares). B, [Ca²⁺]_i increase induced by fMLF or MCT-1 in cells treated with 50 ng/ml PTX for 16 h (open columns) or in control cells (filled columns). C, abilities of hMCT-1 and fMLF to induce β-hexosaminidase release, chemotaxis, and increases in [Ca²⁺]_i were measured in cells treated with 50 ng/ml PTX for 16 h (open columns) or in control cells (filled columns). In C, the effects of fMLF and hMCT-1 on PTX-treated cells are expressed as percentages of those induced by fMLF in the control cells. All data are expressed as mean ± S.E. of five independent experiments. Chem, chemotaxis. D, the expression of Gα_i2 (left) or Gα_q (right) proteins in the undifferentiated (Undiff.) or differentiated (Diff.) cells was analyzed on Western blots using specific antibodies (see “Experimental Procedures”). As positive controls, Gα_i2 and Gα_q proteins in bovine brain membrane were also visualized using the same specific antibodies. memb., membrane.