Perturbation of the secretory network in Closterium acerosum by Na+-selective ionophores

Closterium acerosum possesses a well-defined, mucilage-secretory mechanism consisting of up to 100 Golgi bodies, two distinct vacuolar networks, and a n active cytoplasmic-streaming network located in the cell periphery. Five different sodium-affecting agents were applied to actively secreting cells in order to determine the role, if any, of Na+ on this secretory mechanism. Significant effects to the endomembrane system and actin cytoskeleton were noted upon treatment with the Na+-specific ionophores monensin and SQ1-Et. In particular, the following alterations were noted: incurling of Golgi ci sternae and the formation of circular cisternal profiles at the trans face, swelling of the cis-medial cisternae, and dissociation of the Golgi body f rom the internal cytoplasm to the peripheral cytoplasmic zones. Immunogold labeling with a mucilage-specific polyclonal antibody reveals that mucilage production is diminished during longer ionophore treatments. Likewise, bot h the polar and peripheral vacuoles disintegrate into a series of smaller v acuoles. Cytoplasmic streaming ceases and the normal actin network of the p eripheral cytoplasm transforms into irregularly spaced fibrillar bundles. F inally, multilaminate structures appear at the plasma membrane. No cytologi cal effects could be observed with the Na+-channel blockers or Na+-current transducers QX-14, tetrodotoxin, or amiloride.