細胞内Ca²⁺ストアと血管平滑筋収縮

抄録

The Ca²⁺ release activity of inositol 1, 4, 5-trisphosphate receptor (InsP₃R) is biphasically dependent on the cytoplasmic Ca²⁺ concentration: activation near 100 nM and inhibition around 1 μM. We have found that the cytoplasmic Ca²⁺ concentration is not simply a modulator of InsP₃R but is an indispensable factor for channel activation. The Ca²⁺ requirement of InsP₃R places the Ca²⁺ release channel within a Ca²⁺-mediated positive feedback loop, which has been demonstrated with caged InsP₃ and Ca²⁺. The positive feedback mechanism seems to be the important basis for the generation of Ca²⁺ wave in various cell types including smooth muscle cells. To further clarify the role of Ca²⁺ stores in the smooth muscle function, we measured the Ca²⁺ concentration in individual smooth muscle cells in isolated vascular tissues stimulated with perivascular sympathetic nerves using a confocal microscope. We observed in these cells Ca²⁺ waves/oscillations due to Ca²⁺ release from the stores. These results show that the Ca²⁺ requirement of InsP₃ receptor plays an important role in the regulation of vascular contraction. They also throw new light on both pharmacological and pathophysiological studies of vascular tone.