Ionic conductive properties of rabbit proximal straight tubule basolateral membrane

P. A. Welling, R. G. O'Neil

Research output: Contribution to journalArticlepeer-review


The ionic conductive properties of the nonperfused rabbit proximal straight tubule (S2) basolateral membrane were assessed by microelectrode techniques. The response of the basolateral membrane electrical potential difference, V(bl), to rapid changes in the peritubular bath concentration of K, HCO3, Na, and Cl were monitored with microelectrodes. The control steady-state V(bl) averaged -41 mV (cell negative). An increase in peritubular bathing medium K concentration from 5 to 40 mM resulted in an instantaneous and sustained depolarization of +14.6 mV (27% of ΔE(K)). Addition of barium (2 mM) depolarized the V(bl) by +15.8 mV and abolished the V(bl) response to the high-K medium. In other studies, reduction of peritubular bicarbonate at constant pH from 25 to 2.5 mM instantaneously and transiently depolarized V(bl) by +15.8 mV (26% of ΔE(HCO3)). In these same tubules reduction of peritubular Na from 126 to 2.2 mM resulted in an instantaneous and paradoxical depolarization of V(bl) of +21.5 mV. Both depolarization transients resulting from reduction of Na and HCO3 were simultaneously inhibited by the addition of 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS; 0.5 mM), consistent with the presence of a SITS-sensitive Na-HCO3-coupled conductive pathway. In the absence of the bicarbonate buffer, reduction of Na resulted in a small sustained hyperpolarization of -5.8 mV (5% of ΔE(Na)). Reduction of peritubular Cl from 120 to 4 mM resulted in an instantaneous and sustained depolarization of V(bl) of +5.3 mV (6% of E(Cl)) and was not affected by the addition of bumetanide (0.1 mM). It is concluded that the basolateral membrane of the nonperfused proximal straight tubule is characterized by a major barium-sensitive K conductance and a SITS-sensitive Na-coupled HCO3 conductance that carries net negative charge. These pathways are paralleled by relatively minor, but important, Na-conductive and Cl-conductive pathways.

Original languageEnglish (US)
Pages (from-to)F940-F950
JournalAmerican Journal of Physiology - Renal Fluid and Electrolyte Physiology
Issue number4 27-4
StatePublished - 1990
Externally publishedYes


  • 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid
  • acid/base metabolism
  • barium
  • bumetanide
  • cell volume regulation
  • chloride conductance
  • circuit analysis
  • epithelial ion transport
  • fluid and electrolyte homostasis
  • potassium chloride cotransport
  • potassium conductance
  • sodium conductance
  • sodium-dependent bicarbonate cotransport

ASJC Scopus subject areas

  • Physiology


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