Potentiation by nitric oxide of the ATP-sensitive K⁺ current induced by K⁺ channel openers in guinea-pig ventricular cells

Abstract

1. Modulation by nitric oxide (NO) of the ATP-sensitive K⁺ channel (K_ATP) current (I_K (ATP)) was investigated in single ventricular cells dissociated from guinea-pig hearts. I_K (ATP) was induced by 5-amino-N-[2-(2-chlorophenyl)ethyl]-N′-cyano-3-pyridinecarboxamidine (KRN4884) and cromakalim.

2. In the whole-cell patch clamp configuration, KRN4884 (0.13 μM) increased the outward current in a concentration-dependent manner with an EC₅₀ value of 0.48 μM. This current was completely antagonized by glibenclamide (1 μM).

3. I_K (ATP) induced by either KRN4884 (0.3 μM) or cromakalim (10 μM) was significantly enhanced by the additional application of a NO donor (±)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide (NOR3, 0.1 and 1 mM).

4. The potentiating effect was observed only when NOR3 solution was prepared just before experiments, when release of NO was considered to be on-going. The effect was significantly eliminated in the presence of the NO scavenger oxyhaemoglobin (310 μM). Also, oxidative metabolites of NO, such as NO₂⁻ or NO₃⁻, were without effect.

5. 8-Bromo-guanosine-3′ : 5′-cyclic monophosphate (8-Br-cyclic GMP, 0.10.5 mM) significantly decreased I_K (ATP) induced by KRN4884.

6. In cell-attached patches, NOR3 (1 mM) potentiated the KRN4884-induced I_K (ATP) in a way similar to that seen in whole-cell recordings. By contrast, NOR3 (1 mM) did not enhance the current in either inside-out or outside-out patches.

7. These results indicate that NO potentiates the action of K⁺ channel openers on the K_ATP through a mechanism which remains to be determined.

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