The effect of loop diuretics on Cl‐ transport in smooth muscle of the guinea‐pig vas deferens and taenia from the caecum.

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Abstract
1. The role of Na+, K+, Cl‐ co‐transport, identified in the previous paper (Aickin & Brading, 1990), has been characterized further by investigation of the effects of loop diuretics on Cl‐ movements in the smooth muscle cells of guinea‐pig vas deferens measured by 36Cl fluxes and Cl(‐)‐sensitive microelectrodes. Some flux experiments were also repeated in the taenia from the guinea‐pig caecum. 2. Frusemide (2 mM) reduced the steady‐state Cl‐ content, slowed 36Cl loss into Cl(‐)‐free solution and both slowed and reduced Cl‐ accumulation by Cl(‐)‐depleted cells of the vas deferens. When anion exchange was inhibited by the presence of DIDS, (4,4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid), frusemide further slowed the loss of Cl‐ into Cl(‐)‐free solution, further reduced Cl‐ accumulation such that Cl‐ uptake amounted to a level consistent with a passive distribution and halted the rise in the intracellular Cl‐ activity (aiCl) at levels above about 10 mM. 3. Application of the higher‐affinity loop diuretics bumetanide and piretanide in vas deferns had no significant effect on 36Cl efflux into Cl(‐)‐free solution or on the initial rate of rise of aiCl but reduced the final level attained. In the presence of DIDS, however, both agents further slowed efflux into Cl(‐)‐free solution, and halted the rise in aiCl at levels above about 10 mM. Measurement of greatly slowed intracellular pH transients on removal and readdition of external Cl‐ (Clo‐) in the presence of frusemide suggests that the larger effects of this drug are mediated by inhibition of anion exchange as well as of co‐transport. 4. The relative potency of the loop diuretics, investigated in the presence of DIDS was: bumetanide greater than piretanide greater than frusemide. This sequence was found in both vas deferens, using direct measurement of aiCl, and taenia, using 36Cl uptake. 5. Comparison of data from the vas and taenia showed that 36Cl efflux into Cl(‐)‐free, HCO3(‐)‐free solution was about twice as fast in the taenia, and that bumetanide or piretanide reduced this efflux to about the same rate as that observed in the vas with or without the loop diuretic. DIDS caused a similar absolute reduction of efflux in both preparations. 6. Stimulation of 36Cl efflux on readdition, and inhibition on removal of Nao+ in the presence of DIDS, was much greater in the taenia than in vas and in both preparations was blocked by bumetanide or piretanide.(ABSTRACT TRUNCATED AT 400 WORDS)

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