Abstract
We investigated the mechanisms underlying regulation of contraction with measurements of isometric force and intracellular calcium concentration ([Ca2+] i) in NIH 3T3 fibroblast re-constituted into fibers using a collagen matrix. Treatment with the major phospholipids, neurotransmitters and growth factors had little effect on baseline isometric force. However, U46619, a thromboxane A2 (TXA2) analogue, increased force and [Ca2+] i. 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, SQ29548, abolished the U46619-induced responses. CS-induced contractions are dependent on an intracellular calcium store function; however, the U46619 response depended not only on intracellular calcium stores but also calcium influx from the extracellular medium. Inhibition of Rho kinase suppressed both U46619- and CS-induced responses; in contrast, inhibition of protein kinase C (PKC) reduced only the U46619 response. Moreover, addition of U46619 to a CS contracture enhanced force and [Ca2+] i responses. These results indicate that U46619-induced responses involve both PKC and Rho kinase pathways, in contrast to activation by CS. TXA2 thus 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. [Jpn J Physiol 54 Suppl:S248 (2004)]
