Role of intracellular stored calcium on the generation of spontaneous activity in gastrointestinal smooth muscle

记录豚鼠离体胃肌电反应，产生周期性慢电位，幅度约30 mV，时程5-6个S。慢电位不受河豚毒素或钙拮抗剂的抑制。慢电位可被DIDS或尼氟米酸消除，提示慢电位是通过激活钙敏感的氯通道而产生的。用钙指示剂Fula-2荧光法测定细胞内钙离子浓度表明，慢电位与细胞内钙离子浓度升高有关。细胞内钙通道阻滞剂BAPTA、IP3受体阻断剂2-APB和内源性钙泵阻断剂CPA均可抑制钙反应和慢电位。线粒体原载体(CCCP)或线粒体ATP敏感性钾通道(5-HDA)的抑制剂也可抑制慢电位和钙瞬变的产生。这些结果表明，质子产生的线粒体活性诱导钙敏感酶的激活，最终产生IP3，IP3通过从内库释放而升高细胞内钙浓度，并激活质膜上的钙敏感离子通道。这些过程被认为参与了胃起搏细胞起搏电位的产生。

Recording of electrical responses from the isolated stomach muscles of the guinea-pig produced periodical generation of slow potentials with about 30 mV in amplitude and 5-6 s in duration. Slow potentials were not inhibited by TTX or Ca antagonists. Slow potentials were abolished by DIDS or niflumic acid, suggested that the potentials were produced by activation of Ca-sensitive Cl channels. Measurement of intracellular Ca concentrations by using Ca-indicator fula-2 fluorescence indicated that slow potentials were associated with an increase in intracellular Ca concentrations. Ca-responses, together with slow potentials, were inhibited by BAPTA (an intracellular Ca chilator), 2-APB (an inhibitor of IP3 receptors) and CPA (an inhibitor of internal Ca-pump). Inhibitors of mitochondrial protonophore (CCCP) or mitochondrial ATP-sensitive K-channel (5-HDA) also abolished the generation of slow potentials and Ca-transients. These results suggested that mitochondrial activity produced as a results of proton production induces an activation of Ca-sensitive enzymes and finally produces IP3, which in tern elevates intracellular Ca concentrations by releasing from the internal stores and activates Ca-sensitive ion channels at the plasma membrane. These processes are considered involved in the generation of pacemaker potentials in gastric pacemaker cells.