Electrophysiological Properties of Endogenous Single Ca Activated Cl Channels Induced by Local Ca Entry in HEK293

Microdomains formed by proteins of endoplasmic reticulum and plasma membrane play a key role in store-operated Ca entry (SOCE). Ca release through inositol 1,4,5-trisphosphate receptor (IPR) and subsequent Ca store depletion activate STIM (stromal interaction molecules) proteins, sensors of intraluminal Ca, which, in turn, open the Orai channels in plasma membrane. Downstream to this process could be activated TRPC (transient receptor potential-canonical) calcium permeable channels. Using single channel patch-clamp technique we found that a local Ca entry through TRPC1 channels activated endogenous Ca-activated chloride channels (CaCCs) with properties similar to Anoctamin6 (TMEM16F). Our data suggest that their outward rectification is based on the dependence from membrane potential of both the channel conductance and the channel activity: (1) The conductance of active CaCCs highly depends on the transmembrane potential (from 3 pS at negative potentials till 60 pS at positive potentials); (2) their activity (NPo) is enhanced with increasing Ca concentration and/or transmembrane potential, conversely lowering of intracellular Ca concentration reduced the open state dwell time; (3) CaCC amplitude is only slightly increased by intracellular Ca concentration. Experiments with Ca buffering by EGTA or BAPTA suggest close local arrangement of functional CaCCs and TRPC1 channels. It is supposed that Ca-activated chloride channels are involved in Ca entry microdomains.