Fig. 1.
SLO-2 is activated by EGL-19/CaV1 and by SR calcium release. (A) A schematic model is shown illustrating how EGL-19 and SR calcium release contribute to SLO-2 activation. (B and C) IkhiCl was significantly decreased by Nemadipine (N, an EGL-19 antagonist) and by cyclopiazonic acid (CPA, a SERCA inhibitor). The inhibitory effects of Nemadipine and CPA are eliminated in slo-2 mutants, demonstrating that SLO-2 mediates the K current inhibited by these drugs. Representative traces (B) and mean current density (C) at +30 mV are shown. These results suggest that EGL-19 and SR calcium release are both required for SLO-2 activation. (D–F) IkhiCl was significantly decreased by mutations inactivating UNC-68/RYR and ITR-1/IP3R receptors. Representative traces (D), mean current density (E) at +30 mV, and mean current density ratio recorded with and without CPA treatment (F) are shown. For ITR-1 muscle-specific knockouts [itr-1(mKO)], we utilized a CRE inactivated allele, itr-1(fl), together with a transgene expressing CRE in body muscles. Additive IkhiCl defects were not observed in unc-68;itr-1(mKO) double mutants (E), suggesting that RYR and IP3R receptors function together to promote SLO-2 activation. CPA’s inhibitory effect on IkhiCl was significantly reduced in unc-68 and itr-1(mKO) mutants (F), suggesting that CPA inhibits SLO-2 activation by blocking SR calcium release. (G) SHK-1 (IkloCl) currents were unaffected in unc-68 and itr-1(mKO) mutants. Mean IkloCl current density is plotted as a function of membrane potential. Controls assessing ITR-1 function in the nonexcised itr-1(fl) strain and the effect of muscle CRE expression on IkhiCl currents are shown in SI Appendix, Fig. S1. Values that differ significantly are indicated (ns, not significant; *P < 0.05; ***P < 0.001; ****P < 0.0001). Error bars indicate SEM.