H1-CALPONINSAND H2-CALPONINS ARE NOT ESSENTIAL FOR NOREPINEPHRINE-INDUCED OR SODIUM FLUORIDE-INDUCED CONTRACTION OF RAT AORTIC SMOOTH-MUSCLE

To investigate the controversial issue concerning the role of calponin in smooth muscle contraction, this study examined the relationship be tween smooth muscle calponin and the contraction of aortic rings from different strains of rats: Sprague-Dawley (SD), Wistar, and Wistar Kyo to (WKY). Western blot analysis demonstrated that h1- and h2-calponins are present in aortic smooth muscle from adult SD rats but not Wistar or WKY rats. Nevertheless, h1-calponin is detectable in stomach from Wistar rats, although at a much lower level compared with that in the SD rat stomach. This suggests that a repressed expression of the gene, instead of a simple null mutation, may have caused its absence from t he aortic smooth muscle. Despite the presence or absence of calponin, the aortic smooth muscles from the different strains of rats all devel op contractions in response to the physiological agonist norepinephrin e (NE) and following activation with the plasma membrane receptor-inde pendent NaF induction. The data indicate that h1- and h2-calponins are not essential for NE- and NaF-induced contractions in aortic smooth m uscle. The calponin-positive adult SD rat aorta was found to be more s ensitive in contractile response to NE and NaF inductions compared wit h the calponin-negative rat aortae. This may imply a potential modulat or function of calponin in the contraction of smooth muscle,whereas ot her contractile protein isoform differences between these rat strains may also play a role. (C) Chapman & Hall Ltd.