Early activation of p160ROCK by pressure overload in rat heart

We investigated the mechanisms underlying regulation of contraction with measurements of isometric force and intracellular Ca²⁺ concentration ([Ca²⁺]_i) in NIH 3T3 fibroblast reconstituted into fibers with the use of a collagen matrix. Treatment with the major phospholipids, neurotransmitters, and growth factors had little effect on baseline isometric force. However, U-46619, a thromboxane A₂ (TxA₂) analog, increased force and [Ca²⁺]_i; EC₅₀ values were 11.0 and 10.0 nM, respectively. The time courses were similar to those induced by calf serum (CS), and the maximal force was 65% of a CS-mediated contraction. The selective TxA₂ receptor antagonist SQ-29548 abolished the U-46619-induced responses. CS-induced contractions are dependent on an intracellular Ca²⁺ store function; however, the U-46619 response depended not only on intracellular Ca²⁺ stores, but also on Ca²⁺ influx from the extracellular medium. Inhibition of Rho kinase suppressed U-46619- and CS-induced responses; in contrast, inhibition of C kinase (PKC) reduced only the U-46619 response. Moreover, addition of U-46619 to a CS contracture enhanced force and [Ca²⁺]_i responses. These results indicate that U-46619-induced responses involve PKC and Rho kinase pathways, in contrast to activation by CS. Thus TxA₂ may have a role in not only the initial step of wound repair as an activator of blood coagulation, but also in fibroblast contractility in later stages. collagen matrix; signal transduction; wound repair