Using Arsenazo Ⅲ as a myoplasmic calcium indicator, we have studied the calcium transients evoked by voltage-clamp depolarizing pulses in frog twitch muscle fibres which had been temporarily depolarized by 80 mmol/LK...Using Arsenazo Ⅲ as a myoplasmic calcium indicator, we have studied the calcium transients evoked by voltage-clamp depolarizing pulses in frog twitch muscle fibres which had been temporarily depolarized by 80 mmol/LK^+ in the absence or presence of myoplasmic Li^+. After the high K^+ exposure, for either a short (15 rain) or long(1 h) time, the post-K^+ calcium transients could gradually be restored to the level of the pre-K^+ ones, if the fibres were not loaded with Li^+.In contrast, the post-K^+ calcium transients of Li^+-loaded fibres could not fully recover,and were depressed in a Li^+ concentration-dependent manner.The mean amplitude of the post-K^+ responses recorded more than 3.5 h after 15 min high K^+ exposure was reduced to 56% of pre-K^+ control in the fibres which had been loaded with Li^+ in 20 mmol/L Li^+ Ringer's solution.This depression could be prevented or partially reversed by exogenous myo-inositol.More depression could be induced by 1 h high K^+ exposure, but the presence of exogenous myo-inositol could not clearly prevent the post-K^+ calcium transients from reduction.Assuming that high K^+ exposure caused a depletion of myo-inositol and probably other changes in the metabolism of inositol phospholipids in Li^+ loaded fibres,we conclude that some metabolites of phosphoinositides may play modulation roles in excitation-contraction coupling in frog twitch muscle fibres.展开更多
基金Project supported by the National Natural Science Foundation of China.
文摘Using Arsenazo Ⅲ as a myoplasmic calcium indicator, we have studied the calcium transients evoked by voltage-clamp depolarizing pulses in frog twitch muscle fibres which had been temporarily depolarized by 80 mmol/LK^+ in the absence or presence of myoplasmic Li^+. After the high K^+ exposure, for either a short (15 rain) or long(1 h) time, the post-K^+ calcium transients could gradually be restored to the level of the pre-K^+ ones, if the fibres were not loaded with Li^+.In contrast, the post-K^+ calcium transients of Li^+-loaded fibres could not fully recover,and were depressed in a Li^+ concentration-dependent manner.The mean amplitude of the post-K^+ responses recorded more than 3.5 h after 15 min high K^+ exposure was reduced to 56% of pre-K^+ control in the fibres which had been loaded with Li^+ in 20 mmol/L Li^+ Ringer's solution.This depression could be prevented or partially reversed by exogenous myo-inositol.More depression could be induced by 1 h high K^+ exposure, but the presence of exogenous myo-inositol could not clearly prevent the post-K^+ calcium transients from reduction.Assuming that high K^+ exposure caused a depletion of myo-inositol and probably other changes in the metabolism of inositol phospholipids in Li^+ loaded fibres,we conclude that some metabolites of phosphoinositides may play modulation roles in excitation-contraction coupling in frog twitch muscle fibres.
