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.
Nasu
T
T
Department of Veterinary Pharmacology, Faculty of Agriculture, Yamaguchi University, Japan. nasu@agr.yamaguchi-u.ac.jp
Suzuki
N
N
D000535:Aluminum / Q000493:pharmacokinetics / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics / Q000494:pharmacology; D002412:Cations; D002614:Chelating Agents / Q000494:pharmacology; D003106:Colon / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D003676:Deferoxamine / Q000494:pharmacology; D004347:Drug Interactions; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D011188:Potassium / Q000037:antagonists & inhibitors / Q000494:pharmacology*
D002412:Cations; D002614:Chelating Agents; D000535:Aluminum; D003676:Deferoxamine; D011188:Potassium; D002118:Calcium