Effects of potassium channel opener KRN4884 on human conduit arteries used as coronary bypass grafts

Differential Effects of Gq Protein-Coupled Uridine Receptor Stimulation on IL-8 Production in 1321N1 Human Astrocytoma Cells

G-protein-coupled receptors (GPCRs) trigger various physiological functions. GPCR-mediated effects largely depend on the receptor-associated G-protein subtypes. However, compelling evidence suggests that single receptor proteins activate multiple G-protein subtypes to induce diverse physiological responses. This study compared responses mediated by three different Gq-binding uridine nucleotide receptors, P2Y₂, P2Y₄, and P2Y₆, by measuring Ca²⁺ signaling and interleukin (IL)-8 production. In 1321N1 human astrocytoma cells stably expressing these receptors, agonist stimulation evoked concentration-dependent intracellular Ca²⁺ elevation to a similar extent. In contrast, agonist-induced IL-8 production was prominent in P2Y₆-expressing cells, but not in P2Y₂- and P2Y₄-expressing cells. In addition to inhibition of Gq signaling, G₁₂ signal blockade attenuated uridine 5'-diphosphate (UDP)-induced IL-8 production, suggesting the involvement of a small G-protein pathway. The Rac inhibitor EHop-16 prevented UDP-induced IL-8 release. The P2Y₆-triggered IL-8 production was also inhibited by extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and protein kinase B (Akt) inhibitors. These results suggest that P2Y₆ receptor-induced IL-8 production requires Gq-mediated Ca²⁺ signaling as well as G₁₂-mediated activation of Rac. The results also suggest the importance of considering the involvement of multiple G proteins in understanding GPCR-mediated functions.

Arterial grafts: clinical classification and pharmacological management

In comparison with standard saphenous vein grafts, use of the internal mammary artery (IMA) as a coronary artery bypass graft has achieved superior long-term results. This is related to the differences in the biological characteristics between the venous and arterial grafts. However, even arterial grafts are not uniform in their biological characteristics. The variation in the perioperative behavior of the grafts and in their long-term patency may be related to different characteristics. These factors should be taken into account in the use of arterial grafts, some of which are subjected to more active pharmacological intervention during and after the operation to obtain satisfactory results. To better understand the biological behavior of the grafts, their common features and their differences, a clinical classification may be useful for a practicing surgeon. Based on experimental studies of their vasoreactivity combined with anatomical, physiological and embryological considerations, we have proposed a functional classification for arterial grafts that may be useful clinically. Our classification suggests that there are three types of arterial grafts: Type I-somatic arteries; Type II-splanchnic arteries; and Type III-limb arteries. Type I arteries have enhanced endothelial function and release more nitric oxide and other relaxing factors. Type II arteries, such as the gastro-epiploic artery, and Type III arteries, such as the radial artery (RA), have higher pharmacological reactivity to vasoconstrictors. This classification explains why the IMA has the best long-term patency. Because Type II and III arteries are prone to spasms due to higher contractility, they require more active pharmacological interventions. Furthermore, the harvesting technique of the conduits, including the saphenous vein and IMA, are described and discussed in this article. Prevention of spasms using two cocktails of medications (verapamil + nitroglycerin and nicardipine + nitroglycerin) during harvesting of the conduits is described. These solutions have been demonstrated to be clinically effective.

Effects of KRN4884, a Novel K+ Channel Opener, on Ionic Currents in Rabbit Femoral Arterial Myocytes

Effects of KRN4884 (5-amino-N-[2-(2-chlorophenyl)ethyl]-N'-cyano-3-pyridinecarboxamidine), a novel K(+) channel opener, on ionic currents were examined in rabbit femoral arterial myocytes (RFAMs). Under whole-cell clamp conditions where cells were superfused with 5.9 mM K(+) bathing solution, KRN4884 elicited an outward current at -30 mV. KRN4884-induced current had a reversal potential of -78 mV and was abolished by application of glibenclamide (glib). KRN4884 was approximately 43 times more potent than levcromakalim in activating an ATP-sensitive K(+) current (I(K-ATP)). On the other hand, KRN4884 affected neither voltage-dependent Ca(2+) nor delayed rectifier K(+) channel currents. In the inside-out patch clamp configuration where cells were superfused with the symmetrical 140 mM K(+) solution, KRN4884 activated 47 pS K(+) channels in the presence of adenosine diphosphate. Similar 47 pS K(+) channels, which were reversibly inhibited by glib, were recorded under outside-out patch conditions. Using RT-PCR analysis, we found that inward rectifier K channel 6.1 (Kir6.1) and sulfonylurea 2B (SUR2B) transcripts were predominantly expressed in rabbit femoral artery. These results indicate that KRN4884 potently activates I(K-ATP) in RFAMs. The KRN4884-sensitive 47 pS K(+) channel activity underlying I(K-ATP) is a vascular type K(ATP) channel consisting of Kir6.1 and SUR2B and has similar characteristics to those of ATP-sensitive K(+) channels activated by K(+) channel openers in other types of smooth muscles.

Hypoxic preconditioning in coronary microarteries: role of EDHF and K+ channel openers

BACKGROUND

Hypoxic preconditioning may provide a useful method of myocardial protection in cardiac operations. The present study was designed to investigate the possible mechanisms of preconditioning regarding endothelium-derived hyperpolarizing factor (EDHF) and the effect of a potassium channel opener KRN4884 on the porcine coronary microartery in mimicking hypoxic preconditioning.

METHODS

Porcine coronary microartery rings (diameter 200 to 500 microm) studied in a myograph were divided into seven groups: (1) control group; (2) hypoxia-reoxygenation group (hypoxia for 60 minutes followed by reoxygenation for 30 minutes); (3) preconditioning group (hypoxia for 5 minutes followed by reoxygenation for 10 minutes before hypoxia reoxygenation); (4) KRN4884 pretreatment group (KRN4884 was added into the myograph chamber 20 minutes before hypoxia reoxygenation); (5) 5-hydroxydecanoate + KRN group (5-hydroxydecanoate was given 20 minutes before KRN4884 pretreatetment); (6) glibenclamide (GBC) + KRN group (GBC was added 20 minutes before KRN4884 pretreatment); and (7) endothelium denuded group (the endothelium was removed). The endothelium-derived hyperpolarizing factor-mediated relaxation to bradykinin was studied in the rings precontracted with U46619 in the presence of N(omega)-nitro-L-arginine and indomethacin.

RESULTS

The maximal relaxation induced by bradykinin was reduced in hypoxia reoxygenation (40.7% +/- 2.8% vs 66.9% +/- 2.5% in control, p = 0.000). This reduced relaxation was recovered in either preconditioning (64.6% +/- 4.6%, p = 0.002), or KRN4884 pretreatment (67.1% +/- 3.6%, p = 0.000). The 5-hydroxydecanoate, but not GBC pretreatment abolished the effect of KRN44884 pretreatment (67.1% +/- 3.6% vs 42.9% +/- 3%, p = 0.001).

CONCLUSIONS

Hypoxia reoxygenation reduces the relaxation mediated by endothelium-derived hyperpolarizing factor in the coronary microartery. This function can be restored by either hypoxic preconditioning or the K(ATP) channel opener KRN4884, and therefore K(ATP) channel openers may provide similar effect as preconditioning. The mechanism is mainly related to the mitochondrial ATP-sensitive K+ channels.