Detection of intercellular transfer of cAMP. (A) Cell pair where one cell expressed SpIH-eGFP (green cell) and the other expressed RFP only (red cell). 500 μM cAMP was delivered via patch pipette into the red cell that did not express SpIH and SpIH currents were recorded from cell expressing SpIH in perforated patch mode. Both cells express Cx43. (B) Current recorded from the SpIH-expressing cell, in response to voltage pulses from a holding potential of 0 to −100 mV, returning to a tail potential of +50 mV. The arrow indicates the opening of the patch into whole cell recording mode and the beginning of cAMP delivery into the donor cell. SpIH current over time increased to steady state. The red bar on time axis indicates SpIH current activation time interval t during which current reaches saturation.(C) Segments of SpIH current records when the whole cell patch was opened (*) and 135 s later with saturated current (**).