Selective inhibition of potassium contracture in guinea pig taenia coli by ruthenium red.

Effects of ruthenium red on isotonic KCl induced contracture (K-contracture), cellular 45Ca uptake and 45 Ca binding to surface membranes were examined in the smooth muscle cells of guinea pig taenia coli. These results were compared with those using lanthanum (La3+). The tonic component of the K-contracture was selectively inhibited by 1 mM ruthenium red. In contrast, 1 mM La3+ inhibited the phasic component of the K-contracture to a large extent. Use of 1 mM ruthenium red selectively inhibited the tonic component of K-contracture and caused a marked decrease in cellular 45Ca uptake in that component of K-contracture. In contrast, 1 mM La3+ largely inhibited the phasic component and caused a significant decrease in cellular 45Ca in that component. According to Scatchard plot analysis, there are two kinds of Ca2+ binding sites of high and low affinity, respectively, on the surface membrane of the taenia coli. One mM ruthenium red suppressed those of low affinity more strongly than those of high affinity. In contrast, 1 mM La3+ suppressed high affinity sites more markedly than low affinity sites. Based on these results, it seems possible to conclude that ruthenium red mainly blocks the initial binding sites linked with Ca2+ influx which is related to the production of the tonic component while La3+ blocks those sites related to the phasic component of the K-contracture of guinea pig taenia coli.