ABSTRACT. A high-K + , Na + -deficient (isosmotic 154 mM K + and 0 mM Na + ; I-154 K + ) solution induced contraction followed by gradual relaxation of the smooth muscles of the porcine trachea, while hyperosmotic addition of 65 mM KCl (H-65 K + ) induced a large sustained contraction. The I-154 K + solution also induced a sustained increase in [Ca 2+ ] i level. Decreases in muscle tension and increases in cellular water content were both prevented by the addition of sucrose or NaCl in the porcine trachea. An additional application of phloridzin inhibited recoveries of I-154 K + solution by addition of NaCl in the porcine trachea. Addition of pyruvate or oxaloacetate recovered the I-154 K + solution-induced relaxation in the porcine trachea. Although application of I-154 K + solution did not affect PCr and ATP contents in the bovine trachea, the solution induced a gradual decrease of PCr content in the porcine trachea. Moreover, application of pyruvate or oxaloacetate recovered the I-154 K + solution-induced decreases of PCr content in the porcine trachea. Phloridzin inhibited H-65 K + -induced contraction in porcine, but not in bovine trachea. In conclusion, the I-154 K + solution-induced relaxation in the porcine trachea is probably due to swelling of cells and inhibition of glucose utilization. Moreover, the inhibition of glucose utilization in I-154 K + medium in porcine trachea is different from that of bovine trachea.