Cytoskeletal involvement during hypo-osmotic swelling and volume regulation in cultured chick cardiac myocytes

The membrane skeleton in spherical cardiac myocytes subjected to hypo-osmot ic challenge was examined by laser scanning confocal microscopy. A distinct cortical layer intimately localized under the plasmalemma was revealed for spectrin and actin (including filamentous actin and a-sarcomeric actin). D esmin filaments were abundant and in close contact with the plasmalemma. Du ring swelling and subsequent regulatory volume decrease (RVD) the structura l integrity of these cytoskeletal elements remained intact, and the close a ssociation between actin and plasmalemma persisted as confirmed by double i mmunolabeling. Subplasmalemmal P-tubulin labeling was sparse. Hypo-osmotic conditions disrupted the microtubules and depolymerized tubulin. Neither pr etreatment with taxol nor with colchicine, resulted in any effect on cell v olume regulation. The present results show that actin, desmin, and spectrin contribute to a subplasmalemmal cytoskeletal network in spherical cardiac myocytes, and that this membrane skeleton remains structurally intact durin g swelling and RVD. It is suggested that the integrity of this membrane ske leton is important for stabilization of the plasmalemma and the membrane-in tegrated proteins during hypoosmotic challenge, and that it may participate in the regulation of the cell volume.