Effects of glucose removal and readmission on potassium contracture in the guinea‐pig taenia coli.

Abstract

SUMMARY1. 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.2. The rate of 02 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.3. The effects of glucose removal were rapidly reversed when glucose or ,ihydroxybutyrate (fl-HB) were readmitted to the bathing solution. In the absence of Ca, readmission and removal of the substrates produced an insignificant change in 02 consumption, but the next Ca contraction was potentiated, the effect being stronger with glucose than f-HB.4. 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 ,SM-carbachol, still produced a transient contraction. This suggests that the tonic contraction has disappeared partially because of diminished Ca influx.5. In glycogen-depleted preparations, the depolarization caused by carbachol, or by 20 mM-K, was increased and spike discharge initiated when glucose was readmitted. Verapamil, which scarcely affected the depolarization by carbachol

Effects of readmission of substrate on the membrane potential in glycogen‐depleted guinea‐pig taenia coli.

“…However, in the present experiments, glycogen depletion was probably much more complete compared with the previous experiments, because simple removal of glucose from the external medium reduces tissue glycogen only very slowly (Bueding & Hawkins, 1964;Axelsson et al 1965;Ashoori et al 1984). The very poor appearance of spontaneous SUBSTRATE READMISSION IN SMOOTH MUSCLE spike activity in the present experiments may partly be due to the very severe glycogen depletion and probably also to the much smaller size of the preparation.…”

“…The hyperpolarization gradually converted to a depolarization of about 5 mV on which spike activity appeared. Thus, this electrical response corresponds well to the mechanical response previously observed (Ashoori et al 1984), which was a transient relaxation followed by an increase in tension when substrate was applied to a glycogen-depleted preparation. When the temperature was lowered to 28°C (B), the degree of hyperpolarization was significantly reduced and at 25°C (C), the hyperpolarization disappeared.…”

“…However, the depolarization and spike activity are not significantly affected by removal of either the external Na or K. The depolarization is less dependent on the temperature than the preceding hyperpolarization. Thus, as previously proposed (Ashoori et al 1984), the depolarization is likely to be due to an increase in Ca conductance of the plasma membrane.…”

“…2). As previously shown (Ashoori et al 1984), verapamil (0-1 /SM) blocked the spike activity and the depolarization caused by substrate readmission, revealing the underlying hyperpolarization clearly (A). The was readmitted at 5-9 mM-K, it produced a smaller and slower hyperpolarization compared with the change in membrane potential at 20 mM-K (B).…”

“…The methods used were the same as previously described (Ashoori et al 1984). Guinea-pigs of either sex were used after stunning and bleeding.…”