Inhibitory effects of hexavalent chromium ions on the contraction in ileal longitudinal smooth muscle of guinea-pig.

1. The high-K (60 mM)-induced ileal tonic tensions were not affected after 5 min with (0.01-1 mM) Cr6+. However, they were inhibited dose-dependently by Cr6+ after 30 min application. 2. Cr6+ inhibited the tonic response to K more strongly than the phasic response. 3. Cr6+ did not displace Ca(2+)-concentration-response curves to the right, although it reduced the Ca2+ response size. 4. The low affinity binding sites of Ca2+ and the tissue ATP concentration during K contraction was not entirely inhibited after 5 min with 0.5 mM Cr6+. However, they were fairly inhibited after 30 min with the Cr6+. 5. We suggest that Cr6+ probably reduced tension by the interference of Ca2+ influx at the cell membrane resulting from the inhibitory action on mitochondria.