Effects of High-K⁺, Na⁺-Deficient Solution on Contractility of the Smooth Muscles of the Bovine Trachea

Abstract

A high-K⁺, Na⁺-deficient (I-154 K⁺) solution induced contraction followed by gradual relaxation of the smooth muscles of the bovine trachea, while hyperosmotic addition of 65 mM KCl induced a large sustained contraction. Exposure of the muscle to the I-154 K⁺ solution induced an increase in the ratio of cellular water content and a sustained increase in oxidized flavoprotein fluorescence or reduced pyridine nucleotide fluorescence. The I-154 K⁺ solution also induced a sustained increase in [Ca²⁺]i level. Decreases in developed tension and increases in cellular water content were both prevented by the addition of sucrose or NaCl but not pyruvate. Substitution of KI for KCl in the I-154 K⁺ solution produced a greater inhibition of contraction, while substitution with K-propionate produced no inhibition of contraction. Moreover, decreases in developed tension and increases in cellular water content were both prevented by addition of 100 μM 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS), but not 10 μM bumetanide or 1 mM acetazolamide. In conclusion, I-154 K⁺ solution induced-relaxation in the bovine trachea may be due to swelling of smooth muscle cells and the mechanism of swelling is probably involved in DIDS-sensitive anion movement.