Mechanical response of guinea pig taenia coli in high-K-Na-deficient medium under anoxia.

For investigation of the properties of smooth muscle contraction hypertonically added 40 mm K medium has been used as a routine in this laboratory. Others have used isotonic high K/Na deficient medium for the same purpose. The distinct difference xisting between the mechanical response of guinea pig taenia coli in hyper-40 K medium and that in iso 152 K medium has been reported earlier. The response in hyper-40 K medium consist ed of a phasic and a tonic phase (1). The tonic response in hyper-40 K medium at a steady level was very much higher than that in iso-152 K medium (2). The tissue calcium in hyper-40 K medium increased con siderably above control levels while that in iso-152 K medium decreased sharpely below control levels (2). The "Ca uptake of the fraction which did not exchange within 4 minutes in hyper-40 K medium was also considerably above control while that in iso-152 K medium was not above control (2). The tonic response in hyper-40 K medium has been found to be abolished by factors suppressing sodium transport mechanism or aerobic breakdown of carbohydrates (3), but the nature of this response in iso-152 K medium has not been studied. This small contracture was therefore investigated . Strips of taenia coli isolated from white male guinea pigs were suspended in an organ bath containing Tyrode solution of the following composition (mm) : NaCI 136.8, KCl 2.7, CaCl, 2.5, MgC1, 1.0, NaH,P04 0.4, NaHCO3 11.9 and glucose 5.5, saturated with 95% 02 and 5% CO, mixture at 37°C. Iso-152 K medium was prepared by substituting all sodium ions of normal Tyrode solution by potassium ions. Hyper-40 K me dium was prepared by the addition of KCI crystals to normal Tyrode solution to give a final concentration of 42.7 ms K. Tension changes were recorded isometrically with mechanoelectro-transducer.