Calcium ionophores and tension production in skinned frog muscle fibers.

Antibiotics, X-537A and A23187, were added in micromolar concentrations to selected bathing solutions of skinned frog muscle fibers, and they were shown to affect the production of tension in the skinned fibers. Segments of skinned fibers were bathed in a buffered calcium solution with a pCa near the threshold for contraction. When a segment was moved to a lightly buffered calcium solution with a pCa higher than the threshold for contraction but one containing either antibiotic, a transient contracture of the segment resulted. if the procedure was repeated in the same segment, no contracture was produced. The results are consistent with the idea that the antibiotics function as calcium ionophores in the membrane of the sarcoplasmic reticulum of skinned fibers.