Ng R C, Rouse D, Suki W N
J Clin Invest. 1984 Sep;74(3):834-42. doi: 10.1172/JCI111500.
Calcium transport was studied in isolated S2 segments of rabbit superficial proximal convoluted tubules. 45Ca was added to the perfusate for measurement of lumen-to-bath flux (JlbCa), to the bath for bath-to-lumen flux (JblCa), and to both perfusate and bath for net flux (JnetCa). In these studies, the perfusate consisted of an equilibrium solution that was designed to minimize water flux or electrochemical potential differences (PD). Under these conditions, JlbCa (9.1 +/- 1.0 peq/mm X min) was not different from JblCa (7.3 +/- 1.3 peq/mm X min), and JnetCa was not different from zero, which suggests that calcium transport in the superficial proximal convoluted tubule is due primarily to passive transport. The efflux coefficient was 9.5 +/- 1.2 X 10(-5) cm/s, which was not significantly different from the influx coefficient, 7.0 +/- 1.3 X 10(-5) cm/s. When the PD was made positive or negative with use of different perfusates, net calcium absorption or secretion was demonstrated, respectively, which supports a major role for passive transport. These results indicate that in the superficial proximal convoluted tubule of the rabbit, passive driving forces are the major determinants of calcium transport.
在兔浅表近端曲管的分离S2节段中研究了钙转运。将45Ca添加到灌注液中以测量管腔到浴液的通量（JlbCa），添加到浴液中以测量浴液到管腔的通量（JblCa），并添加到灌注液和浴液中以测量净通量（JnetCa）。在这些研究中，灌注液由一种平衡溶液组成，该溶液旨在使水通量或电化学势差（PD）最小化。在这些条件下，JlbCa（9.1±1.0 peq/mm×min）与JblCa（7.3±1.3 peq/mm×min）无差异，且JnetCa与零无差异，这表明浅表近端曲管中的钙转运主要是由于被动转运。流出系数为9.5±1.2×10（-5）cm/s，与流入系数7.0±1.3×10（-5）cm/s无显著差异。当使用不同的灌注液使PD为正或负时，分别证明了净钙吸收或分泌，这支持了被动转运的主要作用。这些结果表明，在兔的浅表近端曲管中，被动驱动力是钙转运的主要决定因素。
