Figure 4.

Role of K⁺ channel activity in donut formation. (a) Images of mtDsRed-transfected H9c2 cells show that a high concentration valinomycin (Val) causes mitochondria swelling (middle) that is insensitive to CSA (right). (b) Effect of various doses of valinomycin on Opa1 cleavage (b) and on ΔΨ_m (c). Hollow circles show the H9c2 cells treated with valinomycin, whereas the filled symbols show the corresponding time control. (d) Images of mtYFP-expressing (green) and TMRE-loaded H9c2 cells show donut formation by a low concentration valinomycin (0.5 nM) that did not evoke ΔΨ_m loss, Opa1 cleavage and massive matrix swelling. (e) Lack of protection by CSA against valinomycin-induced donut formation. (f and g) Dependence of donut formation during H–R on K⁺ channel opening. The concentrations of drugs were as follows: diazoxide (K_ATP agonist, 100 μM), NS1619 (K_Ca agonist, 30 μM), 5HD (K_ATP inhibitor, 500 μM), paxilline (Pax, K_Ca inhibitor, 10 μM). H9c2 cells were pretreated with drugs for 20 min before hypoxia (H) (^*P⩽0.004)