J.‐L. Bény

Aim: Exogenous ATP elicits a delayed calcium‐independent K⁺current on freshly isolated mouse thoracic aorta myocytes. We investigated the receptor, the intracellular pathway and the nature of this current.Methods: The patch‐clamp technique was used to record ATP‐elicited delayed K⁺current in freshly dissociated myocytes.Results: ATP‐elicited delayed K⁺current was not inhibited by a ‘cocktail’ of K⁺channel blockers (4‐AP, TEA, apamin, charybdotoxin, glibenclamide). The amplitude of the delayed K⁺current decreased after the reduction of extracellular pH from 7.4 to 6.5. These two characteristics suggest that this current could be carried by the TASK subfamily of ‘twin‐pore potassium channels’ (K2P). Purinergic agonists including dATP, but not ADP, activated the delayed K⁺current, indicating that P2Y₁₁is the likely receptor involved in its activation. The PKC activator phorbol ester 12,13‐didecanoate stimulated this current. In addition, the PKC inhibitor Gö 6850 partially inhibited it. Real‐time quantitative PCR showed that the genes encoding TASK‐1 and TASK‐2 are expressed.Conclusion: Our results indicate that blocker cocktail‐insensitive delayed K⁺current in freshly dissociated aortic myocytes is probably carried by the TASK subfamily of twin‐pore channels.

Substance P and bradykinin, endothelium-dependent vasodilators of pig coronary artery, trigger in endothelial cells a rise in cytosolic Ca2+ concentration ([Ca2+]i) and membrane hyperpolarization. The aim of the present study was to determine the type of Ca2+-dependent K+ (KCa) currents underlying the endothelial cell hyperpolarization. The substance P-induced increase in [Ca2+]i was 30 % smaller than that induced by bradykinin, although the two peptides triggered a membrane hyperpolarization of the same amplitude. The two agonists evoked a large outward K+ current of the same conductance at maximal stimulation. Agonists applied together produced the same maximal current amplitude as either one applied alone. Iberiotoxin (50 nM) reduced by about 40 % the K+ current activated by bradykinin without modifying the substance P response. Conversely, apamin (1 μm) inhibited the substance P-induced K+ current by about 65 %, without affecting the bradykinin response. Similar results were obtained on peptide-induced membrane hyperpolarization. Bradykinin-induced, but not substance P-induced, endothelium-dependent relaxation resistant to NG-nitro-L-arginine and indomethacin was partly inhibited by 3 μm 17-octadecynoic acid (17-ODYA), an inhibitor of cytochrome P450 epoxygenase. Similarly, the bradykinin-induced K+ current was reduced by 17-ODYA. Our results show that responses to substance P and bradykinin result in a hyperpolarization due to activation of different KCa currents. A current consistent with the activation of large conductance (BKCa) channels was activated only by bradykinin, whereas a current consistent with the activation of small conductance (SKCa) channels was stimulated only by substance P. The observation that a similar electrical response is produced by different pools of channels implies distinct intracellular pathways leading to KCa current activation.