Cell and luminal activities of chloride, potassium, sodium and protons in the late distal tubule of Necturus kidney.

Abstract

SUMMARY1. Double-barrelled (selective vs. conventional) microelectrodes were used to assess the steady-state activities (a) of the ions Cl-, K+, Na+ and H' in peritubular blood capillaries (abld) and in cell (ace11) and lumen (alum) of the late distal tubule2. acl1, acm and abl were 5-5 + 0-3, 11P8 + 1I0 and 70 5 + 0-1 mm, respectively. They were used to compute the chemical potentials for Cl-across the three diffusive barriers of the tissue. Basolateral and apical membrane potentials were -74-3 + 1 1 and -60-1+2-0 mV, respectively (cell negative); the lumen was thus negative with respect to blood, by 13-6 + 1-5 mV. The electrochemical potential difference (e.p.d.) for Cl-of 42 mV across the apical membrane opposes Cl-absorption, implying active apical Cl-uptake, since Cl-is known to be absorbed in the l.d.t. Basolateral Cl-exit is favoured by an e.p.d. of 10 mV.3. aKe1 a Km and abl were 65-8 + 0-8, 2-5 + 0-1 and 2-5 + 0-1 mm, respectively. The electrochemical distribution of K+ indicates that K+ absorption, if present, proceeds against an adverse apical e.p.d. of 18 mV. Basolateral K+ distribution is close to its electrochemical equilibrium, suggesting high K+ permeability at this membrane.4. aea was 9 0 +0-4 mm, abd 71-0+0-3 mm, and a Na was approximated at about 9 mm. Diffusive Na+ entry from lumen to cell is favoured by an e.p.d. close to 65 mV. Basolateral Na+ exit must be active, since it proceeds against an e.p.d. of 130 mV.5. Cell, luminal and blood pH were 7-14 + 0 03, 6-52 + 0-08 and 7-37 + 0 04, respectively. The luminal electrochemical potential of H+ is higher than that of cell (by 91 mV) and blood (by 34 mV) indicating that proton secretion into the lumen must be active.6. The e.p.d. of each ion across the epithelium opposes, by its orientation, the established direction of net transepithelial ion transport, suggesting that the shunt pathway may serve only for back-diffusion.* The authors' names are in alphabetical order.

Does the colonic H,K-ATPase also act as an Na,K-ATPase?

“…Simultaneous measurements of membrane potential, V m , and intracellular activity of Na ϩ ([Na] i ) or protons (expressed as intracellular pH, pH i ) were performed by using double-barreled (ionselective and conventional) microelectrodes connected to a high impedance electrometer (WPI Instruments FD 223, Waltham, MA). Manufacture of microelectrodes and composition of their filling solutions have been described in detail elsewhere (11). In the present study, as in our previous work (2,12) , where A ref is the ionic activity (in mM) of ion i in the reference solution, and V sel is the electrochemical potential difference (in mV) for i, measured by using the ion-selective barrel of the microelectrode.…”

“…In the latter solution, 90 mM KCl was added to maintain osmolarity and to take into account the slight interference of the high intracellular K ϩ activity value on [Na] i measurements (11). S fell to 35-40 mV in the following mixed solutions: 1 mM NaCl ϩ 99 mM KCl vs. 10 mM NaCl ϩ 90 mM KCl.…”

NH3 Is Involved in the NH4+ Transport Induced by the Functional Expression of the Human Rh C Glycoprotein

“…Intracellular pH Measurements-Intracellular pH (pH i ) and membrane potential (V m ) were simultaneously measured using double-barreled pH-sensitive microelectrodes (filled with the Fluka H ϩ ionophore 95291), as detailed previously (19). The slope, S, of the pH-selective microelectrode was determined before and after each intracellular puncture by measuring the variation of potential induced by a 0.5 pH U change in pH o .…”

Evidence for Activation of Endogenous Transporters in Xenopus laevis Oocytes Expressing the Plasmodium falciparum Chloroquine Resistance Transporter, PfCRT

“…The membrane potential (V m ) and the intracellular pH (pH i ), intracellular Na ϩ activity (␣ Na ), or intracellular Cl Ϫ activity (␣ Cl ) were simultaneously measured using double-barreled ion-selective microelectrodes. The details of microelectrode manufacture have been described previously (32,36). In this study, the tip of the pH-sensitive barrel was filled with Fluka H ϩ ionophore 95291 and its shank with 67 mM NaCl, 40 mM KH 2 PO 4 , and 23 mM NaOH.…”