Communicating junctions and calmodulin: inhibition of electrical uncoupling in Xenopus embryo by calmidazolium.

This paper reports the inhibitory effects of calmidazolium (CDZ), a calmodulin inhibitor, on electrical uncoupling by CO2. Membrane potential and coupling ratio (V2/V1) are measured in two neighboring cells of Xenopus 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 X 10(-8) - 1 X 10(-7) M) strongly inhibits uncoupling. The inhibition starts after 30, 50 and 60 min of treatment with 1 X 10(-7), 7 X 10(-8) and 5 X 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.