Rapidly photoreleased Fe2+ activates BK channels

Catabolism of heme by heme oxygenase results in the liberation of carbon monoxide (CO) and iron ions (Fe²⁺). Studying the impact of both mediators is not straightforward because of rapid diffusion and limited stability. Here we demonstrate that CORM-S1 (dicarbonyl-bis(cysteamine)iron(II)) is a useful chemical that precisely delivers CO and Fe²⁺ when illuminated with blue light. Fe²⁺, rapidly released from CORM-S1 in a flash-photolysis setting, activates BK_Ca channels with an efficacy much higher than CO. BK_Ca channels are therefore downstream targets of heme oxygenase and may connect heme signaling with electrical cell signaling. Physiologically relevant micromolar Fe²⁺ concentrations activate BK_Ca channels as much as unphysiologically high (> 2 mM) Mg²⁺ concentrations.