Communicating junctions and calmodulin: Inhibition of electrical uncoupling inXenopus embryo by calmidazolium

Abstract

This paper reports the inhibitory effects of calmidazolium (CDZ), a calmodulin inhibitor, on electrical uncoupling by CO₂. Membrane potential and coupling ratio (V ₂/V₁) are measured in two neighboring cells ofXenopus embryos (16 to 64 cell stage) for periods as long as 5.5 hr. Upon exposure to 100% CO₂, control cells consistently uncouple even if the CO₂ treatments are repeated every 15 min for 2.5 hr. CDZ (5×10⁻⁸−1×10⁻⁷ m) strongly inhibits uncoupling. The inhibition starts after 30, 50 and 60 min of treatment with 1×10⁻⁷, 7×10⁻⁸ and 5×10⁻⁸ m CDZ, respectively, is concentration-dependent and partially reversible. In the absence of CO₂, CDZ also improves electrical coupling. CDZ has no significant effect on membrane potential and nonjunctional membrane resistance. These data suggest that calmodulin or a calmodulin-like protein participates in the uncoupling mechanism.