The contractile apparatus in vascular smooth muscle cells of spontaneously hypertensive rats possess increased calcium sensitivity: the possible role of protein kinase C.

OBJECTIVE: The purpose of the present investigation was to compare calcium sensitivity of contractile machinery in aorta and portal vein smooth muscle cells (SMC) in normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive Okamoto rats (SHR), and to shed light upon the mechanisms of possible differences.
DESIGN: Investigations into calcium sensitivity of SMC myofilaments can only be made on skinned muscular strips.
METHODS: The vascular strips were made hyperpermeable by detergent skinning with saponin. The isometric calcium-induced contractions of SMC were recorded using a force displacement transducer coupled to a physiograph.
RESULTS: It was shown that the pCa-tension (negative logarithm of calcium concentration versus tension) relationship for aorta and portal vein SMC in SHR shifted to the left in comparison with WKY rats. Putative protein kinase C inhibitors 1-(S-isoquionolinyl-sulfonyll)-2-methylpiperasine (H-7) and polymyxin B shifted the pCa-tension relationship more significantly to the right in the SMC of SHR than in WKY rats. It has also been shown that H-7 and polymyxin B sharply reduced the maximum tension developed by SMC in SHR whilst causing a non-significant decrease in maximum tension of SMC from WKY rats. These results are consistent with higher protein kinase C activity in SMC of SHR.
CONCLUSION: These results indicate that the increase in calcium sensitivity of vascular SMC contractile machinery in SHR may be linked with the increase in their protein kinase C activity.