Fig. 5

Stx4 regulates L-type voltage gated Ca²⁺ channel activity

(A) Heart rates (HRs) determined from ventricular regions of interest of 72 hpf WT and stx4 mutant larvae following a dose-response treatment with 1% DMSO/embryo water (control), 100 nM nifedipine, 1 ?M nifedipine, 2 ?M nifedipine, 5 ?M nifedipine, or 10 ?M nifedipine for 45 min. Data are represented as the mean ± SEM, n = 10?21 larvae/group, one-way ANOVA, ?p < 0.05, ???p < 0.001, ????p < 0.0001.

(B) HRs determined from 72 hpf WT and stx4 mutant larvae treated with either 1% DMSO/embryo water (control) or 20 ?M Bay K-8644. Control stx4 mutants exhibit an ?40% reduction in mean HR versus WT (WT control mean HR: 174.2 bpm, stx4 mutant control mean HR: 104.1 bpm). By contrast, stx4 mutants treated with 20 ?M Bay K-8644 (mean HR: 153.1 bpm) are rescued to ?90% of the WT control HR and ?150% of the untreated stx4 mutant HR, while HR of WTs treated with 20 ?M Bay K-8644 are similar to untreated WT controls (mean HR: 179.3 bpm). Data are represented as the mean ± SEM, n = 20?34 larvae/group, one-way ANOVA, ??p < 0.01, ????p < 0.0001.

(C) HRs determined from WT and stx4 mutant larvae treated with either 1% DMSO/embryo water (control) or a mixture of 10 ?M thapsigargin and 10 mM caffeine (TgC). Data are represented as the mean ± SEM, n = 9?10 larvae/group, one-way ANOVA, ?p < 0.05, ????p < 0.0001.

(D) HRs determined from a dose-response of WT and stx4 mutant larvae treated with either 1% DMSO/embryo water (control), 10 ?M NNC 55-0396, or 20 ?M NNC 55-0396. Data are represented as the mean ± SEM, n = 10 larvae/group, one-way ANOVA, ????p < 0.0001.