The use of lanthanum as a tool to study calcium fluxes in an insect visceral muscle.

1. An ultrastructural study of the effect of lanthanum on an insect visceral muscle is presented. 2. Lanthanum was shown to penetrate the T-tubule system and the dyads, whilst little lanthanum was found bound to the outer sarcolemma. 3. X-ray microanalysis of lanthanum treated muscles showed that lanthanum was able to penetrate the cytoplasm. 4. Lanthanum was found bound to both the outer membranes of mitochondria and the sarcoplasmic reticulum. 5. Caution is therefore expressed in using lanthanum as a tool to study trans-sarcolemmal calcium fluxes in locust visceral muscle.