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Abstract

A new Cl⁻ selective microelectrode based on the ionophore 5,10,15,20-tetraphenyl-21H,23H-porphin manganese(III) chloride is presented which discriminates better against HCO⁻₃ and several organic anions than electrodes containing the Corning 477913 ion-eschanger. Using a redesigned construction procedure, fine-tip double-barrelled microelectrodes were produced which had slopes of −52.4±0.6 mV (SE,n=24), resistances of about 7·10¹¹ Ω and a selectivity coefficient log ^pot_{Cl, HCO3} of −1.40±0.03. Some electrodes showed a small unexplained sensitivity to pH>7.6. When used to puncture cells of isolated S₃ segments of rabbit renal proximal tubule during perfusion with HCO⁻₃ Ringer solution, the electrodes gave a membrane potential of −69.8±1.5 mV and an intracellular Cl⁻ activity, [Cl⁻]_i, of 35.3±2.6 mmol/l. Upon switching bath and lumen perfusions to Cl⁻-free solutions the “residual” [Cl⁻]_i dropped to 1.20±0.03 mmol/l, while in similar measurements with ion-exchanger electrodes the “residual” [Cl⁻]_i dropped only to 10.9±0.5 mmol/l. These observations demonstrate the superiority of the new electrode and prove that previously determined high [Cl⁻]_i values in Cl⁻-free ambient solutions reflect interference problems rather than non-exchangeable intracellular chloride.