| Popis: |
Transport processes in the medullary thick ascending limb of Henle (MTAL) have previously been investigated predominantly using tubule suspensions, perfusion of the loop of Henle in vivo, or individual perfused tubules [1, 2]. One important approach to investigate mechanisms of transport and luminal-basolateral sidedness of ion movement directly has been to isolate highly purified vesicle preparations of both types of plasma membranes of epithelia, such as the renal proximal tubule and the small intestine [reviewed in 3—5]. Regarding the MTAL, however, isolation of luminal (LMV) and basolateral (BLMV) plasma membrane vesicles has posed considerable difficulties, and has generally yielded mixed plasma membrane fractions consisting of both LMV and BLMV [5]. It is also important to remember that most vesicle studies aimed at characterizing transport processes in the MTAL have been performed on plasma membrane vesicles derived either from the entire outer medulla or from outer medullary homogenates [5], and the results then extrapolated to the MTAL. Clearly, for direct investigation into the basic mechanisms of transtubular solute transport in the MTAL, it would be valuable to isolate both types of plasma membranes free of contamination with intracellular as well as with plasma membranes from other nephron segments. In the present paper, we describe a new and simple approach that allowed the simultaneous isolation of LMV and BLMV with high yields from a single homogenate sample of purified isolated rat MTALs. Because this is the first report of the isolation of both types of MTAL plasma membrane vesicles, we wanted to examine whether these membrane preparations may serve as a useful model to characterize the transport properties of the two surfaces of this nephron segment. This report describes our evidence for the expression of different Na/H antiporters on the LMV and BLMV isolated from rat MTAL. |
