Effects of aluminum ions on K(+)-induced contraction in ileal longitudinal smooth muscle

The mechanism of the inhibition of K(+)-induced contraction caused by aluminum ions (Al3+) was analyzed in ileal longitudinal muscle and taenia coli of guinea-pig. Al3+ (2-5 mM) inhibited dose-dependently the high-K+ (60 mM, hypertonic)-induced contraction in ileal muscle. Al3+ reduced the size of the maximal response to Ca2+ without shifting the concentration-response curves to Ca2+ in taenia coli. Al3+ caused a significant decrease in Ca uptake, measured by the lanthanum method, during the K(+)-induced ileal first phase of the response. Following treatment with 5 mM Al3+ for 0.5-20 min, the ileal K(+)-induced contraction returned to a greater extent, after washing with medium containing the chelator deferoxamine, compared to normal medium. However, with increasing duration, > 30 min of Al3+ treatment, the K(+)-induced contraction did not recover, despite washing with deferoxamine. The aluminum in the cells was even more eliminated by washing with deferoxamine when the duration of Al3+ treatment was < 20 min. The present findings indicate that the inhibitory action by Al3+ on K(+)-induced contraction at the shorter treatment (< 20 min) may result from the interference of calcium permeability at the cell membrane in ileal muscle. However, with increasing duration of Al3+ treatment, Al3+ ions accumulate in intracellular compartments where deferoxamine cannot reach, and it may exert an inhibitory action on internal sites in ileal cells.