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

Abstract

The mechanism of the inhibition of K +-induced contraction caused by aluminum ions (Al 3+) was analyzed in ileal longitudinal muscle and taenia coli of guinea-pig. Al 3+ (2–5 mM) inhibited dose-dependently the high-K + (60 mM, hypertonic)-induced contraction in ileal muscle. Al 3+ reduced the size of the maximal response to Ca 2+ without shifting the concentration-response curves to Ca 2+ in taenia coli. Al 3+ 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 Al 3+ 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 Al 3+ 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 Al 3+ treatment was <20 min. The present findings indicate that the inhibitory action by Al 3+ 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 Al 3+ treatment, Al 3+ ions accumulate in intracellular compartments where deferoxamine cannot reach, and it may exert an inhibitory action on internal sites in ileal cells.