Flow dependence of chloride transport in rat S1 proximal tubules
Wong, K.R.; Berry, C.A.; Cogan, M.G.
American Journal of Physiology 269(6 Pt 2): F870-F875
1995
ISSN/ISBN: 0002-9513 PMID: 8594882 Document Number: 440461
These studies examined whether the luminal flow dependency of chloride absorption in the S1 proximal tubule during glomerulotubular balance was due to change in active and/or passive transport of chloride. Using in vivo microperfusion in the Munich-Wistar rat and an essentially pure sodium chloride perfusate (devoid of bicarbonate and organic solutes), we found that an increase in luminal perfusion rate from 30 to 45 nl/min caused stimulation of total chloride absorption (active plus passive) by 87 peq cntdot mm-1 cntdot min-1 (632 +- 17 to 719 +- 11, P lt 0.001). When cyanide was added to this perfusate to eliminate active transport, the flow-induced change in passive transport was 58 peq cntdot mm-1 cntdot min-1 (479 +- 9 to 537 +- 11, P lt 0.001). The cyanide-inhibitable active transport component was therefore 29 peq cntdot mm-1 cntdot min-1. With elimination of the transepithelial chloride gradient and, hence, passive transport by isethionate substitution, active transport increased by 63 peq cntdot mm-1 cntdot min-1 (121 +- 4 to 184 +- 7, P lt 0.001) as flow rate rose from 30 to 45 nl/min. Removal of organic solutes from a glomerular ultrafiltrate-like perfusate had a minimal effect on flow-induced change in chloride transport (190 vs. 207 peq cntdot mm-1 cntdot min-1). In conclusion, flow-dependent active and passive chloride transport in the S1 proximal tubule may both contribute to normal glomerulotubular balance.