Extracellular protons modulate the Ca2+block of a Ca2+-blockable monovalent cation channel in chick embryo

✍ Scribed by Robert Sabovcik; Jinqing Li; Pavel Kucera; Blaise Prod'hom

• Publisher: Springer
• Year: 1995
• Tongue: English
• Weight: 327 KB
• Volume: 430
• Category: Article
• ISSN: 0031-6768
• DOI: 10.1007/bf00373900

✦ Synopsis

Some epithelial nonselective cation channels although in an open conformation are impermeable because they are blocked by exlracellular Ca 2~ ions. Such a channel is present in the apical membrane of the ectodermal cells of the chick gastrula. This single-channel study shows that protonation of a site located inside the pore of this embryonic channel reduces the Ca 2" block thus allowing Na + to pass. The apparent pK for Ca 2, at -50 mV shifts from 5.7 at pH 7.4 to 3.5 at pH 4.5. Unexpectedly, the change in Ca 2, affinity does not originate from a destabilization of the binding but comes from a large reduction of the association rate.