| Popis: |
The purpose of this article is to review the literature regarding the characteristics of the gastric parietal cell apical membrane K+ channel and provide new evidence that suggests that the inward rectifying K+ channel, Kir2.1, may be involved in K+ recycling at the apical membrane of the gastric parietal cell. It has been previously reported that gastric H+/K+ ATPase-containing vesicles exhibit a 10 pS K+ channel when measured in planar lipid bilayers. The native gastric K+ channel in these vesicles is insensitive to ATP, is active in the absence of Ca2+, is stable at an extracellular pH of 3.0, and is activated by PKA. A literature search suggested that Kir2.1 has many of the properties of this channel. This is the first report to show that recombinant rabbit Kir2.1 K+ channels are active in the presence of ATP, in the absence of Ca2+, and are stable at an extracellular pH of 3.0. Preliminary results demonstrate that Kir2.1 is also PKA activated. Kir2.1 also exhibits single channel currents that are of similar magnitude as the native channel under these conditions. In an accompanying paper, Grahammer et al suggest from 293 B inhibition of acid secretion that KCNQ1 is the K+ channel involved in K+ recycling at the apical membrane. Kir2.1 is not inhibited by 293B. Acid accumulation by H+/K+ ATPase-containing vesicles from stimulated rabbits is insensitive to 293B. This finding strongly suggests that KCNQ1 is not involved in K+ recycling at the apical membrane of the gastric parietal cell. Kir2.1 is a candidate for this process. |
