Animal cells connected by nanotubes can be electrically coupled through interposed gap-junction channels

TLDR

Tunneling nanotubes (TNTs) are F‑actin–containing membrane tubes that connect cells over long distances and enable intercellular exchange of small molecules and organelles. The authors show that TNTs enable bidirectional electrical coupling between distant animal cells, a process that depends on TNT length and number, requires gap‑junction channels (connexin 43), and triggers voltage‑dependent calcium influx through low‑voltage‑gated Ca²⁺ channels, indicating that TNT‑mediated electrical synchronization activates downstream signaling.

Abstract

Tunneling nanotubes (TNTs) are recently discovered conduits for a previously unrecognized form of cell-to-cell communication. These nanoscale, F-actin-containing membrane tubes connect cells over long distances and facilitate the intercellular exchange of small molecules and organelles. Using optical membrane-potential measurements combined with mechanical stimulation and whole-cell patch-clamp recording, we demonstrate that TNTs mediate the bidirectional spread of electrical signals between TNT-connected normal rat kidney cells over distances of 10 to 70 μm. Similar results were obtained for other cell types, suggesting that electrical coupling via TNTs may be a widespread characteristic of animal cells. Strength of electrical coupling depended on the length and number of TNT connections. Several lines of evidence implicate a role for gap junctions in this long-distance electrical coupling: punctate connexin 43 immunoreactivity was frequently detected at one end of TNTs, and electrical coupling was voltage-sensitive and inhibited by meclofenamic acid, a gap-junction blocker. Cell types lacking gap junctions did not show TNT-dependent electrical coupling, which suggests that TNT-mediated electrical signals are transmitted through gap junctions at a membrane interface between the TNT and one cell of the connected pair. Measurements of the fluorescent calcium indicator X-rhod-1 revealed that TNT-mediated depolarization elicited threshold-dependent, transient calcium signals in HEK293 cells. These signals were inhibited by the voltage-gated Ca(2+) channel blocker mibefradil, suggesting they were generated via influx of calcium through low voltage-gated Ca(2+) channels. Taken together, our data suggest a unique role for TNTs, whereby electrical synchronization between distant cells leads to activation of downstream target signaling.