Characteristic of myosin from peritubular myoid cells

D. FERNÁNDEZ, L.GÓMEZ, V. BERTOLDI, E. CALLEGARI, L. A. LOPEZ

Washington, DC, USA

Congreso; ng The American Society for Cell Biology, 47 th Annual Meeti; 2007

The American Society for Cell Biology

In the mammalian testis, peritubular myoid cells (PMCs) surround seminiferous tubules. These cells are contractile and express the cytoskeletal markers of true smooth muscle, such as alpha-isoactin and F-actin, and participate in the contraction of seminiferous tubules during the transport of spermatozoa and testicular fluid to the rete testis. The goal of this work was to analyze the properties of myosin from PMCs. Myosin from PMCs (PMC-myosin) was isolated from adult rat testis and purified by cycles of aggregation-disaggregation and sucrose gradient centrifugation. PMC-myosin was recognized by a monoclonal anti-smooth muscle myosin antibody, and the peptide sequence shared partial homology with rat smooth muscle myosin-II (SMM-II). A fraction (9 5 %) of PMC-myosin was found soluble in the PMC cytosol, and purified PMC-myosin did not assemble into filaments in the in vitro salt dialysis assay at 4 °C, but did at 20 °C. PMC-myosin filaments are stable to ionic strength to the same degree as gizzard SMM-II filaments, but PMC-myosin filaments were more unstable in the presence of ATP. When PMCs were induced to contract by endothelin-1, a fraction of the PMC-myosin assembled into filaments. From these results we infer that PMCs express an isoform of smooth muscle myosin II, that is characterized by solubility at physiological ionic strength, a requirement for high temperature to assemble into filaments in vitro, and instability at low ATP concentrations. PMC-myosin is part of the PMC contraction apparatus and assembles into filaments when PMCs are induced to contract by hormone.