筋小胞体のカルシウム遊離機構

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Mechanism of calcium release from fragmented sarcoplasmic reticulum vesicles (FRS) was extensively studied. When the ionic composition of SRF was changed from KMS (potassium methanesulfonate) to KCl with maintaining the osmolarity, calcium ions were released from SRF. This ionic exchange is considered to make the membrane potential of inside of the vesicles more negative, namely depolarization. To elucidate that this ionic exchange truely causes the membrane potential change, ionic permeabilities of various ions were determined. Many important ions, such as K+ or Cl-, permeate too fast to follow the permeation by a usual tracer method. The permeability was determined by following the osmotic volume change. As a result, permeation times of various ions were determined. The following are typical results: K+ 20, Cl- 0.4, and MS- 20 in seconds at room temperature. These values show that Cl- permeates 50 times faster than K+ or MS-. This result supports the concept that the membrane potential was depolarized by the ionic exchange from KMS to KCl. Finally, calcium binding sites of SRF were determined by discriminating the sidedness. Two types of sites on the outside and four types of sites on the inside were observed. When the relation between calcium release and the state of bound calcium was compared, it was suggested that the released calcium from FRS by depolarization was originated from that bound to calsequestrin inside the vesicles.
日本生物物理学会の論文

筋小胞体のカルシウム遊離機構

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