Figure 3.

Cx50 Channels are permeable to Ca²⁺ ions. A cell pair expressing Cx50 (A), showed a strong fluorescent response in cell 1 (B, red line), when the pipette attached to cell 1 was opened to release 2 mM Ca²⁺ into the cytoplasm. Cell 2 showed a rise in fluorescent intensity (B, green line) that reached a peak within 10 seconds after Ca²⁺ was delivered to cell 1. Simultaneous measurement of gap junctional currents (C) showed that Cx50 was gated by Ca²⁺ on a much slower time scale than the solute permeation. A less than 50% decline in the Cx50 junctional current was seen 60 seconds after 2 mM Ca²⁺ was delivered to cell 1, which increased to a 77% decline in coupling at 180 seconds. An expanded portion of the record (red asterisk) showed that junctional currents remained stable for many seconds after peak Ca²⁺transfer had occurred.