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It has recently been suggested that rho A and rho kinase (ROK) play a role in the increase in the Ca2+ sensitivity of the smooth muscle myofilaments. In the present study, we investigated the mRNA expressions of rho A and two types of ROK (alpha and beta) in the myometrium obtained from both non-pregnant and pregnant rats. Reverse transcription polymerase chain reaction (RT-PCR) experiments using total RNA from these tissue specimens and the specific primers revealed rho A and both types of ROK mRNAs to be expressed in the rat myometrium. The mRNA expressions of rho A, ROK alpha and ROK beta in the pregnant myometrium were found to increase in comparison to those in the non-pregnant myometrium. These results thus support the idea that the up-regulation of these proteins might be involved in the mechanism underlying the increased contractility of the pregnant myometrium.

It has recently been indicated that rho A and rho kinase may be involved in the mechanism for the increase in Ca2+sensitivity in smooth muscle myofilaments. In the present study, we investigated the mRNA expression of rho A and rho kinase in porcine vascular smooth muscle cells (aorta, coronary artery, pulmonary artery, and pulmonary vein). In reverse transcription–polymerase chain reaction (RT–PCR) experiments, using total RNA from these tissue specimens and the primers designed in the conserved regions of each mRNA in human and bovine, rho A and rho kinase mRNAs were detected in all of these smooth muscle cells. An analysis of these PCR products by direct sequencing indicated that they were derived from each mRNA. The finding that both rho A and rho kinase mRNAs were expressed in the various porcine vascular smooth muscle cells strongly supports the idea that these proteins are involved in the mechanism dealing with the increase in Ca2+sensitivity in the myofilaments of vascular smooth muscle cells.

Using reverse transcription polymerase chain reaction (RT-PCR), we determined the expression of the mRNAs for basic calponin isoforms, namely h 1 and h 2 forms, in the porcine aortic endothelial cells (PAECs) and aortic smooth muscle cells (PASMCs). The mRNAs for both h 1 and h 2 calponin isoforms were expressed in PAECs as well as in PASMCs. However, the expression of h 2 isoform mRNA was more abundant than h 1 isoform in PAECs, while h 1 isoform was more abundant than h 2 in PASMCs. These findings indicated the existence of calponin mRNA and the predominance of h 2 over h 1 calponin isoform in PAECs. It is suggested that h 2 as well as h 1 , calponin isoform might have a physiological role in vascular endothelial cell. This is the first report which describes the existence of calponin h 2 -dominant cells.