Single Ca²⁺-activated nonselective cation channels in neuroblastoma

Abstract

Recent work suggests an important role for intracellular agents in controlling ion channels in the membranes of nerve cells and other excitable tissues. Calcium ions^1,2, cyclic nucleotides³ and protein kinases^4,5 can all act on the inner surface of the membrane to influence ion channel activity. Earlier studies of these effects on intact cells could not, however, effectively control or measure conditions on the inner membrane surface. The technique of recording from detached membrane patches^6,7permits free access to the intracellular face of ion channels and makes it possible to study them in isolation from the many components of the cytoplasm. With this technique, I have studied the response of membrane patches from neuroblastoma cells to intracellular Ca²⁺ ions, and have found a class of nonselective cation channels activated by micromolar concentrations of Ca²⁺ on the intracellular face of the membrane. These channels are almost equally permeable to Na⁺, K⁺, Li⁺ and Cs⁺ ions, but are practically impermeable to Ca²⁺ ions. Similar channels were first found recently in cultured heart cells⁸, where they probably account for the previously reported ‘transient inward’ current⁹. Their discovery in neuronal cells as well as heart cells suggests that this hitherto scarcely recognized channel species may be more widely distributed than previously supposed.