ATP-sensitive K⁺ channels in smooth muscle cells of guinea-pig mesenteric lymphatics: role in nitric oxide and β-adrenoceptor agonist-induced hyperpolarizations

Abstract

1. Intracellular microelectrode recordings were performed to investigate the membrane K⁺ conductances involved in smooth muscle hyperpolarization of lymphatic vessels in the guinea-pig mesentery.

2. Nitric oxide (NO), released either by the endothelium after acetylcholine (ACh; 10 μM) stimulation or by sodium nitroprusside (SNP; 50–100 μM), hyperpolarized lymphatic smooth muscle. These responses were inhibited with the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazole [4,3-a]quinoxalin-1-one (ODQ, 10 μM).

3. ACh and SNP-induced hyperpolarizations were inhibited (by about 90%) upon application of the ATP-sensitive K⁺(K_ATP) channel blocker, glibenclamide (10 μM), or with 4-aminopyridine (2.5 mM), but were not affected by the Ca²⁺-activated K⁺ channels blocker, penitrem A (100 nM).

4. Hyperpolarization caused by the K⁺ channel opener, cromakalim (0.1–10 μM), isoprenaline (0.1 μM) or forskolin (0.5 μM) were all significantly blocked by glibenclamide.

5. Hyperpolarization evoked by ACh and SNP were inhibited with N-[2-(p-bromociannamylamino)-ethyl]-5-isoquinolinesulfonamide-dichloride (H89, 10 μM), suggesting the involvement of cyclic AMP dependent protein kinase (PKA).

6. These results suggest that K_ATP channels play a central role in lymphatic smooth muscle hyperpolarization evoked by a NO-induced increase in cyclic GMP synthesis, as well as by β-adrenoceptor-mediated production of cyclic AMP. Interestingly, both pathways lead to K_ATP channels opening through the activation of PKA.

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