bms-191011 and iberiotoxin

Methylglyoxal, a highly reactive dicarbonyl compound, is formed as a by-product of glycolysis and plays an important role in the pathogenesis of diabetic complications, including diabetic retinopathy. However, it remains to be determined how methylglyoxal affects the regulatory mechanisms of retinal blood flow. In this study, we examined the effects of methylglyoxal on β

Topics: Adrenergic beta-2 Receptor Agonists; Adrenergic beta-2 Receptor Antagonists; Albuterol; Animals; Arterioles; Calcium Channel Agonists; Calcium Channel Blockers; Colforsin; Dose-Response Relationship, Drug; GTP-Binding Protein alpha Subunits, Gs; Injections, Intravenous; Intravitreal Injections; Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; Male; Oxadiazoles; Peptides; Pyruvaldehyde; Rats, Sprague-Dawley; Receptors, Adrenergic, beta-2; Retina; Retinal Vessels; Vasodilation; Vasodilator Agents

We studied the contribution of large conductance Ca(2+)-activated potassium channels (BKCa) in the mechanisms of neuromodulatory effects of anti-inflammatory cytokine IL-10 on hypoxiainduced changes in activity of CA1 pyramidal neurons in rat hippocampus. We used the method of registration of population spikes from CA1 pyramidal neurons in hippocampal slices before, during, and after exposure to short-term episodes of hypoxia. Selective blocker (iberiotoxin) and selective activator of BKCa (BMS-191011) were used to evaluate the contribution of these channels in the mechanisms of suppressive effects of IL-10 on changes in neuronal activity during hypoxia and development of post-hypoxic hyperexcitability. It was shown that BKCa are involved in the modulatory effects of IL-10 on hypoxia-induced suppression of activity of CA1 pyramidal neurons in the hippocampus and development of post-hypoxic hyperexcitability in these neurons.

Topics: Animals; Cell Hypoxia; Hippocampus; Interleukin-10; Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; Oxadiazoles; Peptides; Pyramidal Cells; Rats; Rats, Wistar

The large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels modulate the retinal vascular tone, but question of whether the impairment of the channel function contributes to abnormalities of retinal circulation has not yet been completely elucidated. The purpose of this study was to examine effects of diabetes on the vasodilation induced by activation of BK(Ca) channels. Male Wistar rats were treated with streptozotocin and experiments were performed 2 weeks later. The streptozotocin-treated animals were given drinking water containing 5% d-glucose to shorten the term in the development of retinal vascular dysfunction. The retinal vascular responses were assessed by measuring diameter of retinal arterioles in the fundus images that were captured with an original fundus camera system. In non-diabetic rats, vasodilator effects of acetylcholine on retinal arterioles were significantly reduced by iberiotoxin, an inhibitor of BK(Ca) channels. However, the inhibitory effect of iberiotoxin was not observed in diabetic rats, and the responses to the BK(Ca) channel opener BMS-191011 were almost completely abolished. The retinal vasodilator response to acetylcholine, possibly an endothelium-derived hyperpolarizing factor-mediated response, observed after treatment with N(G)-nitro-l-arginine methyl ester and indomethacin was markedly reduced in diabetic rats. The responses to pinacidil, an opener of ATP-sensitive K(+) channels, were unchanged. These results suggest that the retinal vasodilator response mediated through mechanisms involving activation of BK(Ca) channels is diminished at the early stage of diabetes in rats. The impairment of BK(Ca) channel function may contribute to abnormal retinal hemodynamics in diabetes and consequently play an important role in the pathogenesis of diabetic retinopathy.

Topics: Acetylcholine; Animals; Blood Glucose; Blood Pressure; Cyclooxygenase Inhibitors; Diabetes Mellitus, Experimental; Fluorescein Angiography; Glucose; Heart Rate; Hyperglycemia; Indomethacin; Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Oxadiazoles; Peptides; Pinacidil; Potassium Channels; Rats; Rats, Wistar; Retinal Artery; Vasodilation; Vasodilator Agents

The vascular endothelium plays an important role in regulating retinal blood flow via actions of several vasodilators, including nitric oxide (NO), prostaglandin I₂, and an endothelium-derived hyperpolarizing factor (EDHF). Our previous in vivo studies demonstrated that acetylcholine (ACh) dilates the rat retinal arteriole partly through NO- and prostaglandin-independent pathway, possibly the EDHF-mediated pathway, but the underlying mechanism(s) remains to be elucidated. It has been suggested that activation of Ca²+-activated K+ (K(Ca)) channels contributes to the EDHF-mediated responses; therefore, the roles of K(Ca) channels in ACh-induced vasodilation of retinal arterioles were examined in rats. The retinal vascular responses were assessed by determining changes in diameters of retinal arterioles in ocular fundus images that were captured with an original fundus camera system. Intravitreal injection of charybdotoxin, an inhibitor of intermediate- and large-conductance K(Ca) (I/BK(Ca)) channels, or iberiotoxin, an inhibitor of large-conductance K(Ca) (BK(Ca)) channels, significantly reduced the ACh-induced vasodilation of retinal arterioles, whereas neither apamin, an inhibitor of small-conductance K(Ca) (SK(Ca)) channels, nor TRAM-34, an inhibitor of intermediate-conductance K(Ca) (IK(Ca)) channels, altered the response. The vasodilator response to ACh observed under the combined blockade of NO synthase and cyclooxygenase with N(G)-nitro-L-arginine methyl ester plus indomethacin was also diminished by iberiotoxin. Iberiotoxin did not affect the NO donor NOR3-induced vasodilation of retinal arterioles, whereas it significantly reduced the BK(Ca) channel opener BMS-191011-induced responses. These results suggest that activation of BK(Ca) channels is involved in the EDHF-mediated component of the vasodilator response to ACh in the rat retinal arterioles in vivo.

Topics: Acetylcholine; Animals; Apamin; Arterioles; Blood Pressure; Calcium Channel Agonists; Calcium Channel Blockers; Charybdotoxin; Heart Rate; Hydroxylamines; Indomethacin; Intermediate-Conductance Calcium-Activated Potassium Channels; Large-Conductance Calcium-Activated Potassium Channels; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide Donors; Nitro Compounds; Oxadiazoles; Peptides; Potassium Channels, Calcium-Activated; Pyrazoles; Rats; Rats, Wistar; Retinal Artery; Small-Conductance Calcium-Activated Potassium Channels; Vasodilation