Functional importance of the actin cytoskeleton in contraction of XXXX iris sphincter muscle.

@entity2389 @entity3812 @entity11119 @entity291 @entity5402
1. The contractile capacity of smooth muscle cells depends on the cytoskeletal framework of the cell. The aim of this study was to determine the functional importance of both the actin and the tubulin components of the cytoskeleton in contractile responses of the @entity291 isolated iris sphincter muscle. 2. In each preparation, two contractions to the muscarinic agonist @entity5402 were obtained. The maximum responses of the first contractions were taken as 100%. The second contractions to @entity5402 were elicited in the presence of either @entity2389 (50 and 5 microm), an inhibitor of the actin cytoskeleton, or @entity3812 (100 microm), an inhibitor of the tubulin cytoskeleton (30 min incubation). 3. @entity2389 , at a concentration of 50 microm, significantly decreased the contractions induced by @entity5402 , with the maximum response reduced to 21.8 +/- 6.6% (n = 12) of the initial maximum. The maximal contractions to @entity5402 in the presence of @entity3812 reached 96.2 +/- 7.9% (n = 9) of the initial contraction, which was not significantly different from control second responses to @entity5402 with neither drug present, which reached 113.3 +/- 7.6% (n = 7). 4. The effect of @entity2389 was dose-dependent, since at a lower concentration of 5 microm, the drug decreased the maximum contraction to @entity5402 to 60.3 +/- 8.8% (n = 6). The effect of @entity2389 was at least partially reversible, since after the use of the higher concentration of 50 microm, contractions to @entity5402 increased to 62.3 +/- 15.5% (n = 4) of the maximal response, after 1 h repeated washing of the preparations. 5. @entity11119 , at a concentration of 50 microm, completely abolished the contractions induced by @entity5402 (n = 4). 6. These findings suggest that in @entity291 iris sphincter muscle, contractions to @entity5402 are highly dependent, from a functional point of view, on actin polymerization, and not, to any important degree, on the polymerization of tubulin.
