Burdyga T V, Wray S
The Physiological Laboratory, The University of Liverpool, Crown Street, Liverpool, L69 3BX, UK.
Pflugers Arch. 1998 Oct;436(5):801-3. doi: 10.1007/s004240050705.
To investigate the role of myosin light chain kinase (MLCK) in phasic contractions of intact smooth muscle, we have applied Wortmannin, an MLCK inhibitor, to strips of guinea-pig ureter. Simultaneous measurements of electrical activity, intracellular [Ca2+] ([Ca2+]i) and phasic force showed that Wortmannin (1-4 microM) abolishes force with little or no change in [Ca2+]i and electrical activity. High-K+-induced force production was also abolished by Wortmannin. The effects of Wortmannin were dose dependent - at lower concentrations (100 nM) Wortmannin reduced phasic contractility by 40-50%. It also significantly increased the delay between the Ca2+ peak and force production. These data show that, in phasic smooth muscle, inhibition of MLCK causes contraction to fail, despite normal electrical activity and Ca2+ transients. Our results also indicate that Wortmannin has no secondary effects and that other means of producing force, independent of myosin phosphorylation, are negligible in this tissue. The increased lag between the rise of Ca2+ and force production when MLCK is inhibited was surprising and suggests that post-phosphorylation steps may play a larger role in the delay than was previously considered.
为了研究肌球蛋白轻链激酶（MLCK）在完整平滑肌相性收缩中的作用，我们将MLCK抑制剂渥曼青霉素应用于豚鼠输尿管条。对电活动、细胞内[Ca2+]（[Ca2+]i）和相性张力的同步测量表明，渥曼青霉素（1 - 4 microM）可消除张力，而[Ca2+]i和电活动几乎没有变化。渥曼青霉素也能消除高钾诱导的张力产生。渥曼青霉素的作用呈剂量依赖性——在较低浓度（100 nM）时，渥曼青霉素可使相性收缩力降低40 - 50%。它还显著增加了Ca2+峰值与张力产生之间的延迟。这些数据表明，在相性平滑肌中，抑制MLCK会导致收缩失败，尽管电活动和Ca2+瞬变正常。我们的结果还表明，渥曼青霉素没有继发性作用，并且在该组织中，其他独立于肌球蛋白磷酸化的产生张力的方式可忽略不计。当MLCK被抑制时，Ca2+升高与张力产生之间延迟的增加令人惊讶，这表明磷酸化后步骤在延迟中可能比之前认为的起更大作用。
