Comparison of the pH-sensitivity of Ca2+-activated ATPase in myofibrils from vertebrate and invertebrate striated muscles

摘要

The Ca2+-activation profile of the ATPase of myofibrillar preparations from vertebrate and invertebrate striated muscles was investigated at three different pHs (pH 7.4, 6.8, 6.2). The examination of myofibrils from vertebrate muscles (four fast skeletal, two slow skeletal and four cardiac muscles) showed that the Ca2+-sensitivity always decreased as the pH decreased and the difference in the Ca2+-sensitivity of pH 7.4-pH 6.2 (pH-sensitivity) was the largest in cardiac myofibrils, the smallest in slow skeletal myofibrils and intermediate in fast skeletal myofibrils. The partial pi-I-sensitivity of pH 6.8-pH 6.2 was larger than that of pH 6.8-pH 6.2 in the case of slow skeletal myofibrils, whereas the partial pH-sensitivity of both pH 7.4-pH 6.8 and pH 6.8-pH 6.2 was almost the same in both the cardiac and fast skeletal myofibrils. The myofibrils from invertebrate (two crustacean and two molluscan) striated muscles also showed a decrease in the Ca2+-sensitivity by lowering pH. The overall pH-sensitivity (pH 7.4-pH 6.2) was slightly smaller than that in the cardiac myofibrils. The partial pH-sensitivity of pH 7.4-pH 6.8 was larger than that of pH 6.8-pH 6.2. The profiles of the pH-sensitivity of the invertebrate striated muscles was therefore different from those of vertebrate striated muscles.