RESUMEN
The Na+/H+ antiporter in vacuolar membranes transports Na+ from the cytoplasm to vacuoles using a pH gradient generated by proton pumps, which could reduce Na+ toxicity. It is uncertain that whether the woody plants have the same mechanism. Through differential centrifugation and sucrose density gradient centrifugation, tonoplast vesicles were isolated from Populus tremula calli broken by blender. After establishing pH gradient by V-ATPase, Na+ could dissipate the pH gradient, which indicates that there is Na+/H+ antiporter in the tonoplast vesicles from Populus tremula calli (Km=11.4 mmol/L). Amiloride could inhibit the Na+/H+ antiporter activity. The antiporter could transport Na+ and K+, the affinity for Na+ is higher. Salt stress decreased Km and Vmax.
RESUMEN
It is generally believed that sphingomyelin- and cholesterol-enriched microdomains can be isolated as detergent-resistant membranes (DRMs) from plasma membrane and organelle membranes. Here the isolation of microdomains from porcine cardiac sarcoplasmic reticulum (SR) membranes is described. These SR-derived detergent-resistant membranes (SR-DRMs) enriched in sphingomyelin and cholesterol have a low buoyant density. Both ganglioside GM1 and caveolin-3 in the SR, known as a marker protein of caveolae at plasma membrane are present in the SR-DRMs. It was demonstrated that significant amount of SERCAs together with caveolin-3 associates with SR-DRMs, and are fully functional. The results suggested that SR membranes like other biomembranes,such as the plasma membrane, contained microdomains.