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The effects of removal and readmission of substrates on the K contracture were investigated in the guinea-pig taenia coli. When, after exposure to excess K in Ca-free and glucose-free medium, the readmission and removal of 2.4 mM-Ca were repeated at regular intervals, the Ca-induced contractions decreased progressively. The decrease was more marked in the late than in the early part of the tension response. The rate of O2 consumption decreased when the normal medium was replaced by glucose-free, Ca-free, excess-K solution, but substantially recovered following Ca readmission. ATP and creatine phosphate contents decreased during the Ca-induced contraction, but recovered partially during the subsequent relaxation in Ca-free solution. The effects of glucose removal were rapidly reversed when glucose or beta-hydroxybutyrate (beta-HB) were readmitted to the bathing solution. In the absence of Ca, readmission and removal of the substrates produced an insignificant change in O2 consumption, but the next Ca contraction was potentiated, the effect being stronger with glucose than beta-HB. When the tonic contraction evoked by 2.4 mM-Ca readmission had been abolished in glucose-free, high-K solution, a rise of the external Ca concentration to 10 mM, or 5 microM-carbachol, still produced a transient contraction. This suggests that the tonic contraction has disappeared partially because of diminished Ca influx. In glycogen-depleted preparations, the depolarization caused by carbachol, or by 20 mM-K, was increased and spike discharge initiated when glucose was readmitted.(ABSTRACT TRUNCATED AT 250 WORDS)

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