Enhanced stretch-induced myogenic tone in the basilar artery of spontaneously hypertensive rats

We investigated if the magnitude of myogenic tone in the basilar artery of SHR differs from that in WKY and, if so, whether RhoA- or PKC-dependent mechanisms were involved. Myogenic tone was developed in response to stretch. Stretch-induced myogenic contraction was significantly greater in the SHR than WKY in the presence of external Ca²⁺. However, in the absence of external Ca²⁺, stretch did not evoke a myogenic tone. The [Ca ²⁺]_i-induced contraction was larger in SHR than WKY and the [Ca²⁺]_i-force curve was significantly shifted to the left in SHR compared to WKY. Y-27632 significantly inhibited stretch-induced myogenic tone, but the inhibitory effect was larger in the SHR than WKY. However, PKC inhibitors had no significant effect on the myogenic tone. RhoA and PKCε were expressed at higher levels in the SHR compared to the WKY. RhoA and PKCα translocated from the cytosol to the cell membrane in response to stretch in both animals, but PKCε was translocated only in SHR. Our results strongly suggest that stretch-induced myogenic tone is enhanced in SHR, and the activation of RhoA/Rho kinase plays an important role in the enhanced myogenic tone in SHR.