Impact of Mitochondrial Ca2+-Sensitive Potassium (mBKCa) Channels in Sildenafil-Induced Cardioprotection in Rats

Abstract

BackgroundMitochondrial large-conductance Ca2+-sensitive potassium (mBKCa) channels are involved in myocardial ischemic preconditioning. Their role in sildenafil-induced cardioprotection is unknown. We investigated whether sildenafil-induced acute cardioprotection is mediated by activation of mBKCa channels in the rat heart in vitro.MethodsMale Wistar rats (n = 8 per group) were randomized and anesthetized with pentobarbital (90 mg/kg). Hearts were isolated, mounted on a Langendorff system and perfused with Krebs-Henseleit buffer at a constant pressure of 80 mmHg. Hearts underwent 30 min of global ischemia followed by 60 min of reperfusion. At the end of the experiments infarct size was determined by TTC staining. In the control group rats were not further treated. Sildenafil (3 μM) was administered over 10 min before the beginning of ischemia. The mBKCa channel inhibitor paxilline (1 μM) was administered with and without sildenafil before the onset of ischemia. The pathway underlying sildenafil-induced cardioprotection was further investigated with the protein kinase G blocker KT5823 (1 μM). Myocardial cGMP concentration was measured by ELISA. Data (mean±SD) were analysed with a one and two-way analysis of variance as appropriate.ResultsIn control animals infarct size was 52±8%. Sildenafil increased cGMP concentration and reduced infarct size to 35±6% (P<0.05 vs. control). Paxilline and KT5823 completely blocked sildenafil-induced cardioprotection (paxilline+sildenafil: 50±8%, KT5823+sildenafil: 45±8%; both P<0.05 vs. sildenafil). Functional heart parameters and coronary flow were not different between the study groups.ConclusionThis study shows that in male rats protein kinase G-dependent opening of mBKCa channels plays a pivotal role in sildenafil-induced cardioprotection.

Sildenafil potentiates the antitumor activity of cisplatin by induction of apoptosis and inhibition of proliferation and angiogenesis

“…Due to the unexpected side effect of improvement of penile erection, in 1998, sildenafil citrate (Viagra ® ; Pfizer, Inc., New York, NY, USA) became the first PDE-5 inhibitor for the treatment of erectile dysfunction 8. Recently, sildenafil has shown benefits in experimental cardiac dysfunctions,9,10 tissue injury,11–13 cystic fibrosis,14 and ischemia/reperfusion injury 15,16. Additionally, sildenafil as well as other PDE-5 inhibitors were shown to induce apoptosis in different human tumors, such as colon carcinoma and chronic lymphocyte leukemia 17,18.…”

Activation of PKG and Akt Is Required for Cardioprotection by Ramelteon-Induced Preconditioning and Is Located Upstream of mKCa-Channels

“…Surgical preparation was performed as described previously [13,34]. Briefly, male Wistar rats were anesthetized by intraperitoneal injection of 90 mg/kg pentobarbital and decapitated.…”

“…Previously, we demonstrated that the lowest cardioprotective concentration of Ramelteon is 0.03 µM [8]. The concentration of the respective inhibitors of PKG (KT5823) and Akt (MK2206) was taken from the literature [13,23]. The inhibitors and Ramelteon were administered before global ischemia and reperfusion ( Figure 3A).…”

“…Ramelteon (Ram): Hearts were perfused with 0.03 µM Ramelteon for 10 min. KT5823+Ramelteon (KT + Ram): Hearts were perfused with 1 µM KT5823 [13] combined with 0.03 µM Ramelteon for 10 min.…”

“…The second part of the study was designed to determine the precise sequence of PKG and Akt in the signal transduction pathway of Ramelteon-induced preconditioning ( Figure 3B). The concentration of the activators (BAY60-2770 and NS1619) and inhibitors (MK2206 and KT5823) were taken from the literature [13,23,27]. The substances were administered before global ischemia and reperfusion rat hearts were randomly assigned to five experimental groups (n = 6 per group): Control (Con): Hearts were perfused with Krebs-Henseleit solution for 10 min.…”