Intracellular chloride activity increases in guinea pig ventricular muscle during simulated ischemia

We investigated the effects of simulated ischemia on intracellular Cl− activity ([Cl−]i) in isolated guinea pig ventricular papillary muscles using ion-selective microelectrode techniques. Simulated ischemia in ventricular muscles was produced by stopping the flow of superfusion and immersing preparations in mineral oil as previously described [B. Vanheel, L. Leybaert, A. De Hemptinne, and I. Leusen. Am. J. Physiol. 257 ( Cell Physiol. 26): C365–C379, 1989; Z. F. Lai, J. Liu, and K. Nishi. Jpn. J. Pharmacol. 72: 161–174, 1996]. When preparations were exposed to paraffin oil for 15 min, [Cl−]imarkedly increased and the peak magnitude of [Cl−]ireached 55.3 ± 2.5 mM from 18.7 ± 3.5 mM, whereas membrane potentials ( V m) depolarized from −82.5 ± 1.1 to −54.7 ± 2.4 mV ( n = 6 muscles from 6 animals). SITS (0.5 mM), a known blocker of the Cl−/[Formula: see text]exchanger, suppressed the ischemia-induced depolarization of V m and delayed the onset of the ischemia-induced increase in [Cl−]ibut did not suppress the magnitude of the increase of [Cl−]i. Under Cl−-free conditions created by replacing Cl−with equimolar gluconate, the increase in [Cl−]iduring ischemia was transient and suppressed by >60% compared with that in normal-Cl− conditions (peak value was 20.3 ± 1.7 mM, n = 6 muscles from 6 animals). The present results provide direct evidence that [Cl−]iin ventricular muscle increases in ischemic conditions in quiescent guinea pig ventricular muscle, suggesting that activation of the Cl−/[Formula: see text]exchanger by ischemia would partially contribute to the elevation of [Cl−]iduring the initial stage of ischemia.

Intracellular chloride activity of rabbit proximal straight tubule perfused in vitro

To examine the cellular mechanism of Cl- transport in the proximal tubule, cell Cl- activity (aiCl) was measured with double-barreled Cl(-)-selective microelectrodes in the rabbit proximal straight tubules (PST) perfused in vitro. When tubules were perfused and bathed with ultrafiltrate-like solution, aiCl (corrected for the interference from undetermined intracellular anions, 4.2 mM) was 17.8 +/- 0.5 mM (n = 90), and this value was 1.3 times higher than that predicted from passive distribution (basolateral membrane potential, Vbl = -51.9 +/- 0.8 mV). Reducing either luminal or bath Cl- indicated that the basolateral membrane plays a more important role as a determinant of aiCl. aiCl reduction rates induced by luminal Cl- removal was inhibited by 75% by 1 mM SITS added to the lumen but was not inhibited by furosemide (0.1 mM). Application of SITS in the lumen in the control condition, however, did not change aiCl appreciably. Reducing the luminal HCO3- from 25 to 5 mM did not significantly change aiCl or Vbl. Replacing luminal Na+ with choline decreased aiCl but these effects were still present when luminal Cl- was absent. We conclude that in the rabbit PST: 1) Cl- is taken up into the cell against the electrochemical gradient, 2) the basolateral membrane plays a more important role in the regulation of aiCl, and 3) luminal Cl- transport is SITS sensitive and Na+ independent.