CALDESMON INHIBITS ACTIVE CROSSBRIDGES IN UNSTIMULATED VASCULAR SMOOTH-MUSCLE - AN ANTISENSE OLIGODEOXYNUCLEOTIDE APPROACH

Caldesmon is a thin-filament-associated protein believed to be importa nt in the regulation of smooth muscle contraction, although the precis e mechanism is unknown. We used antisense oligodeoxynucleotides to pro duce intact swine carotid smooth muscle tissue deficient in h-caldesmo n. Caldesmon content was decreased by 78% after 7 days in culture with antisense oligodeoxynucleotides but was unchanged in tissues in the p resence of sense oligodeoxynucleotides or vehicle. Antisense oligodeox ynucleotides produced a significant decrease in the caldesmon/actin ra tio, but no change was measured in the calponin/actin ratio, suggestin g that the effect was specific to caldesmon and not other thin-filamen t-associated proteins. Basal and KCl-stimulated levels of myosin light chain phosphorylation were not different among tissues from all 3 gro ups. In contrast, h-caldesmon-deficient tissues produced 62% less KCl- induced force than controls. Unstimulated h-caldesmon-deficient smooth muscle tissues stretched and then released, redeveloped force, demons trating active crossbridge cycling; strips containing normal h-caldesm on content did not redevelop force on release. We suggest that in rest ing vascular smooth muscle, active crossbridges are inhibited by calde smon. Therefore, regulation of smooth muscle includes a thin-filament- based disinhibition component.