Figure 6. Type II TBC [Ca²⁺]_i Signaling is Normal Whereas ATP Release is Abolished in Calhm1^–/– and Calhm3^–/– Mice.

(A,B) [Ca²⁺]_i signaling is normal in type II TBC from Calhm1^–/– and Calhm3^–/– mice. (A) Representative fura-2 fluorescence ratios in single GFP-positive (type II) (upper traces) and GFP-negative (lower traces) cells in response to 3-min exposure to a cocktail of bitter and sweet compounds in WT, Calhm1^–/– and Calhm3^–/– mice. (B) Summary of fura-2 ratio responses for WT (n = 22, 4 experiments), Calhm1^–/– (n = 16, 6 experiments) and Calhm3^–/– (n = 18, 5 experiments) type II cells. No differences observed among genotypes (two-tailed Student's unpaired t-test, Calhm1^–/– versus WT: P = 0.944, t₃₆ = 0.071; P = 0.547, t₃₆ = 0.607; P = 0.367, t₃₆ = 0.915 and Calhm3^–/– versus WT: P = 0.432, t₃₈ = 0.794; P = 0.930, t₃₈ = 0.088; P = 0.509, t₃₈ = 0.667, for peak, basal and plateau Ca²⁺ signaling, respectively). The basal [Ca²⁺]_i were calibrated as 97 ± 25 nM, 102 ± 7 nM and 87 ± 18 nM for WT, Calhm1^–/– and Calhm3^–/– mice, respectively. Data presented as mean ± s.e.m.; *P < 0.01, **P < 0.001, ***P < 0.0001.

(C) Tastant cocktail- and bath solution-evoked ATP release from gustatory CVP tissue and non-gustatory lingual epithelium (LE). Bitter/sweet taste mixture elicits marked ATP release from CVP versus LE in WT mice (n = 10; two-tailed Student's unpaired t-test, P = 0.0000003, t₁₈ = 8.073). This is abolished in both Calhm3^–/– (n = 5) and Calhm1^–/– (n = 5) mice (two-tailed Student's unpaired t-test, Calhm3^–/– versus WT: P = 0.00023, t₁₃ = 5.023; Calhm1^–/– versus WT, P = 0.00068, t₁₃ = 4.433). ATP was significantly released from CVP tissue by bitter/sweet taste-mixture stimulation (n = 10, WT) compared with response to bath solution (n = 20, including Calhm1^–/– and Calhm3^–/– ; two-tailed Student's unpaired t-test, P = 0.000000001, t₂₈ = 8.153, **P <0.01; ** P <0.001.