ATP-sensitive K⁺ channels (Kir6.1/SUR1) regulate gap junctional coupling in cochlear-supporting cells

Using the double whole-cell patch-clamp technique, we found that the absence of intracellular ATP led to gap junction uncoupling in cochlear-supporting Hensen cells. The uncoupling was observed as a progressive reduction of the gap junctional electrical conductance from a starting value of approximately 40 nS to less than 0.04 nS within 10–20 min. The conductance rundown was partly avoided by at least 3 mM ATP and completely suppressed by 5 mM ATP or 5ʹ-adenylyl-imidodiphosphate (AMP-PNP), the non-hydrolysable ATP analog, in the pipette filling solution, suggesting that ATP was needed as ligand and not as a hydrolysable energy supplier or substrate for enzymatic reactions. The effect of intracellular ATP was mimicked by the external application of barium, a nonselective blocker of inwardly rectifying K⁺ (Kir) channels, and glibenclamide, an inhibitor of the ATP-sensitive Kir channels (K_ATP). Moreover a Ba²⁺-sensitive whole-cell inward current was observed in absence of internal ATP. We propose that the internal ATP kept the K_ATP channels in a closed state, thereby maintaining the gap junction coupling of Hensen cells. The immunostaining of guinea pig cochlear tissue revealed for the first time the expression of the K_ATP channel subunits Kir6.1 and SUR1 in Hensen cells and supported the proposed hypothesis. The results suggest that K_ATP channels, as regulator of the gap junction coupling in Hensen cells, could be the physiological link between the metabolic state of the supporting cells and K⁺ recycling in the organ of Corti.