A monoclonal antitroponin-T cross-reacts with smooth muscle and nonmuscle cells

A mouse monoclonal antibody was prepared against chicken skeletal troponin-T. Indirect immunofluorescence microscopy of smooth muscle and nonmuscle cells indicated the presence of a cross-reactive component(s). In contrast to the definitive I-band reactivity in striated muscle, the smooth muscle components from chicken gizzard, lung, and small intestine showed diffuse, cytoplasmic staining. A filamentous pattern which converged on a perinuclear focus was observed in interphase cells (356 fibroblasts). This cross-reaction was determined to be associated with microtubules. To assess the extent of occurrence of the cross-reactive species, representatives of both the fungal and plant kingdoms were examined. In both Dictyostelium discoideum and cells of the onion (Allium) root tip, the antitroponin-T detected cross-reactive components associated with microtubules. Immunoblot experiments conducted to determine the molecular specificity of the antibody showed cross-reaction with only troponin-T in striated muscle preparations. Similar experiments with the antitroponin-T on chicken gizzard smooth muscle indicated reactivity with two bands whose electrophoretic mobilities are within the range reported for striated muscle troponin-T. Our results indicate the presence of a highly conserved troponin-T cross-reactive determinant in all muscle types, as well as nonmuscle cells. They raise the possibility of a troponin-like molecule in smooth muscle and nonmuscle cells which may confer calcium sensitivity in their cellular filament systems.