Microelectrode measurement of intracellular chloride activity in smooth muscle cells of guinea-pig ureter.

The intracellular Cl activity (aiCl) of smooth muscle cells in the guinea-pig ureter was measured using double-barrelled Cl-sensitive microelectrodes. The mean aiCl in normal Krebs solution was 51.1 mM, equivalent to an ECl of -18.6 mV, with a mean Em of -48.7 mV. Thus aiCl was three times higher than predicted from a passive distribution, aiCl exceeded the extracellular activity by nearly 10 mM in 10%-Cl solution. Complete removal of extracellular Cl (Cl0) caused a decline in aiCl to an apparent level of 3.3 mM with a mean time constant of 6.7 min. Cl ions were reaccumulated against their electrochemical gradient on readmission of Cl0 with a mean time constant of 6.6 min. Both the reaccumulation and loss of Cl ions on changing Cl0 were slowed about three-fold by the presence of the anion exchange inhibitor DIDS. It is therefore concluded that most of the transmembrane Cl movements are mediated by a reversible anion exchange carrier and that PCl is very low. These results are similar to those obtained in vas deferens and may be a general feature of smooth muscle cells.