Small and Intermediate Calcium-Activated Potassium Channel Openers Improve Rat Endothelial and Erectile Function

Abstract

Modulation of endothelial calcium-activated potassium (KCa) channels has been proposed as an approach to restore endothelial function. The present study investigated whether novel openers of KCa channels with small (KCa2.x) and intermediate (KCa3.1) conductance, NS309 and NS4591, improve endothelium-dependent relaxation and erectile function. Rat corpus cavernosum (CC) strips were mounted for isometric tension recording and processed for immunoblotting. Mean arterial pressure (MAP), intracavernosal pressure (ICP), and electrocardiographic (ECG) measurements were conducted in anesthetized rats. Immunoblotting revealed the presence of KCa2.3 and large KCa conductance (KCa1.1) channels in the corpus cavernosum. NS309 and NS4591 increased current in CC endothelial cells in whole cell patch clamp experiments. Relaxation induced by NS309 (<1 μM) was inhibited by endothelial cell removal and high extracellular potassium. An inhibitor of nitric oxide (NO) synthase, and blockers of KCa2.x and KCa1.1 channels, apamin and iberiotoxin also inhibited NS309 relaxation. Incubation with NS309 (0.5 μM) markedly enhanced acetylcholine relaxation. Basal erectile function (ICP/MAP) increased during administration of NS309. Increases in ICP/MAP after cavernous nerve stimulation with NS309 were unchanged, whereas NS4591 significantly improved erectile function. Administration of NS309 and NS4591 caused small changes in the electrocardiogram, but neither arrhythmic events nor prolongation of the QTc interval were observed. The present study suggests that openers of KCa2.x and KCa3.1 channels improve endothelial and erectile function. The effects of NS309 and NS4591 on heart rate and ECG are small, but will require additional safety studies before evaluating whether activation of KCa2.3 channels has a potential for treatment of erectile dysfunction.

Effect of low androgen levels on IKca and SKca3 channels in rat penile corpus cavernosum

“…Meanwhile, in immunohistochemical detection, it was found that SKca3 was highly expressed in endothelial cells and smooth muscle cells, while IKca showed slightly low expression in the endothelial cells and little expression in the smooth muscle cells in corpus cavernosum of rats. These results were in general agreement with previous studies (Comerma‐Steffensen et al., ). Blocking SKca3 and IKca channels in the retinal artery of pigs weakened the effective activation of eNOS and reduced the bioactivity of eNOS, leading to decrease in the production of endothelial NO and reduction of NO‐dependent vasodilation (Gaete, Lillo, Ardiles, Perez, & Figueroa, ).…”

“…As the levels of expression of SKca3 and IKca declined in diseases such as primary hypertension, type 2 diabetic vascular disease, atherosclerosis, heart failure and chronic renal failure, the EDHF‐mediated endothelium‐dependent vasodilation decreased (Angulo et al., ; Chlopicki et al., ; Garland & Dora, ; Kohler et al., ). Recent studies have found that SKca3 and IKca are detected in endothelium and smooth muscle cells of rat corpus cavernosum and openers of KCa2.x and KCa3.1 channels can improve endothelial and erectile function (Comerma‐Steffensen, Carvacho, Hedegaard, & Simonsen, ). Meanwhile, Ca 2+ ‐activated potassium channels' family consists of at least three subtypes with different conductance capacities.…”

Endothelium‐dependent relaxation mechanisms involve nitric oxide and prostanoids in the isolated bovine digital vein

“…Under this experimental condition, acetylcholine was still able to relax the preparation and this effect was reduced by the combination of L‐NAME and indomethacin. A limitation of this experimental approach is that DKS could need a further adrenergic activation to abolish all possible potassium channel activation, like calcium activated potassium channels (K Ca ) in the preparation, as others had shown in the subcutaneous resistance arteries and corpus cavernosum (Comerma‐Steffensen, Carvacho, Hedegaard, & Simonsen, ; Padmanabhan, Jardine, McGrath, & Connell, ). Nonetheless, the effect of specific inhibitors of the proposed EDH pathways was not included in this study, it seems that the contribution of EDH in the isolated bovine digital vein is either scarce or represent a minor supplement to the release of nitric oxide and the endothelium‐derived prostanoids.…”

Ionic Channels as Potential Therapeutic Targets for Erectile Dysfunction: A Review

“…In addition, stimulation of the cavernous nerve improved the erectile function of animals with SK3 overexpression, while this effect was reduced in SK3 downregulation animals ( Comerma-Steffensen S. et al., 2017 ). Furthermore, the relaxation of strips of the corpus cavernosum of mice, induced by NS309, was significantly reduced by the removal of endothelial cells, the use of NO synthase blockers and the use of apamine, which reflects the influence of these channels on endothelial and erectile functions ( Comerma-Steffensen S. G. et al., 2017 ).…”