Ekblad E B, Licko V
Cardiovascular Research Institute, University of California, San Francisco 94143.
Biochim Biophys Acta. 1990 Aug 13;1054(1):41-8. doi: 10.1016/0167-4889(90)90203-p.
Removal of potassium from the nutrient solution of a gastric mucosa results in monotonic decline in acid secretion rate. When potassium is added back to the nutrient solution, acid secretion recovers. In both spontaneously and sub-maximally secreting tissue the recovery of the acid secretion rate takes the form of a transient overshoot above the baseline such that the amount of suppressed acid in the absence of potassium is equal to the amount of acid that is secreted above baseline once potassium is added back. The index of conservation r is zero, i.e., the effect is conservative. In maximally secreting tissue the secretion rate only returns to pre-inhibitory level without an overshoot. The net effect is nonconservative with r = -1. Conservative effect under maximally stimulating conditions was unmasked by exposing the tissue to a stimulus for a specific length of time and comparing amount of acid secreted when nutrient potassium was present with amount of acid secreted when potassium was removed and then added back to the nutrient solution. Stimulation with forskolin is not expressed in the absence of potassium but is unmasked once potassium is added back to the nutrient solution. The conclusion is: removing potassium from the nutrient side inhibits proton translocation by decreasing Vmax and/or increasing Km but is without effect on the formation of acid. Adding potassium back restores the parameter(s) for the translocation step.
从胃黏膜的营养液中去除钾会导致酸分泌速率单调下降。当向营养液中重新添加钾时，酸分泌会恢复。在自发分泌和次最大分泌的组织中，酸分泌速率的恢复都表现为在基线之上出现短暂的超调，使得在无钾情况下被抑制的酸量等于重新添加钾后分泌的超过基线的酸量。守恒指数r为零，即该效应是保守的。在最大分泌的组织中，分泌速率仅恢复到抑制前水平，没有超调。净效应是非保守的，r = -1。通过将组织暴露于特定时长的刺激下，并比较营养液中存在钾时分泌的酸量与去除钾后再添加回营养液时分泌的酸量，最大刺激条件下的保守效应得以显现。在无钾时，福司可林刺激不会表现出来，但一旦向营养液中添加钾，其刺激作用就会显现。结论是：从营养液一侧去除钾通过降低Vmax和/或增加Km来抑制质子转运，但对酸的形成没有影响。重新添加钾可恢复转运步骤的参数。
