The effects of bicarbonate and foreign anions on chloride transport in smooth muscle of the guinea‐pig vas deferens.

Abstract

SUMMARY1. The selectivity of the external site of the Cl transporting mechanism in the guinea-pig vas deferens has been investigated by measurement of 36Cl uptake and efflux and by direct measurement of intracellular pH.2. Replacing 50 % of the Cl in normal Krebs solution inhibited the 15 min uptake of 36C1 in the order NO3 > Br > SCN > F > I > glucuronate, both in Cl-depleted tissues and tissues pre-incubated in the 50 %-Cl solutions (steady-state uptake). After 3 h incubation in these solutions, the total cellular Cl was reduced by the anions in the order Br > NO3 > I > SCN > F > glucuronate. Br, NO3 and I reduced the cellular Cl to less than 50 % of normal, suggesting that they are actively taken up by the cells.3. The ability of foreign anions to inhibit a 3 min uptake of high specific activity, low concentration Cl (6-5 mM) suggests an apparent affinity series of NO3 > Cl = SCN = Br > I > F at the external site.4. Addition of NO3, Cl, Br, HCO3, F, SCN or I to a Cl-free, nominally HCO3-free bathing solution accelerated 36CI efflux. The first four mentioned were powerful stimulants, the other three less potent. However, the exact position of HCO3 in the sequence is uncertain. The rapidity with which CO2 crosses the membrane and forms HCO3 intracellularly may allow competition between HCO3 and Cl at the internal site and so distort the result. The action of F is also questionable since this ion drastically reduces the divalent cation activity and is a metabolic inhibitor.5. Measurement of intracellular pH provided conclusive evidence that Cl, NO3, Br and I can exchange with HCO3 across the cell membrane. This exchange is as rapid with NO3 as with Cl but slower with Br and considerably slower with I. The results also indicate that SCN ions cross the cell membrane.6. It is concluded that Cl, HCO3, Br and NO3 are all translocated by the exchange carrier. I and perhaps SCN also interact with the transport mechanism, but the translocation rate is then greatly reduced. The precise order of the affinity of these anions remains uncertain but the following sequence: NO3 > Cl = SCN = Br >

The effects of anions on fluid reabsorption from the proximal convoluted tubule of the rat.

“…In spite of the low reabsorptive rate, all the anions studied were able to support fluid transport to some extent. When arranged in order of ability to support fluid transport the sequence was very similar to anion permeability sequences of a variety of nerve and muscle membranes (Wright & Diamond, 1977;Aickin & Brading, 1985) and the ability to support fluid transport by the gall bladder epithelium (Whitlock & Wheeler, 1967).…”

Calcium‐stimulated sodium efflux from rabbit vascular smooth muscle.

“…Furthermore, in many cell systems, the Na+-H+ exchanger, implicated in pH regulation (for review see Aronson, 1985) is inhibited by amiloride with a relatively high affinity, inhibition being seen in the 10-100 /M range (Aickin & Thomas, 1977;Aronson, Suhm & Nee, 1983). Smooth muscle cells have an anion exchange system which shows striking similarities to the erythrocyte system (Aickin & Brading, 1985). The red cell anion exchange system has both an exchange mode and a much smaller conductance pathway which are both inhibited by stilbene disulphonic acids (Kaplan, Scorah, Fasold & Passow, 1976;Kaplan, Pring & Passow, 1983).…”