Endotoxemia is associated with impaired diaphragm contractility, and increased nitric oxide (NO) production has recently been implicated in this phenomenon. However, the precise nature of sepsis-related alterations in diaphragm myofiber function remains unclear. We tested the hypothesis that enhanced NO synthesis during sepsis produces diaphragm sarcolemmal injury with attendant abnormalities of myofiber membrane electrophysiology. Two different rat sepsis models were employed: acute (4 h) intraarterial endotoxin (LPS; 20 mg/kg) and subacute (24 h) peritonitis induced by cecal ligation and perforation (CLP). Diaphragm damage occurred after both LPS and CLP, as indicated by hyperpermeability of myofibers to a low molecular weight tracer dye, which is normally unable to penetrate the sarcolemma. Sarcolemmal injury was significantly correlated with reductions in the resting membrane potential (Em) of single diaphragm myofibers. Western analysis revealed increased diaphragmatic expression of the inducible isoform of NO synthase (iNOS) after LPS and CLP. An inhibitor of NOS activity, LNMMA, significantly decreased morphologic as well as electrophysiologic signs of myofiber membrane injury and dysfunction. Therefore, we conclude that both acute endotoxemia and subacute peritonitis models of sepsis lead to significant sarcolemmal damage and altered Em in diaphragm myofibers. These changes appear to be mediated, at least in part, through the pathway of increased nitric oxide production.

Cardiac fibroblasts are involved in the maintenance of myocardial tissue structure. However, little is known about ion currents in human cardiac fibroblasts. It has been recently reported that cardiac fibroblasts can interact electrically with cardiomyocytes through gap junctions. Ca(2+)-activated K(+) currents (I (K[Ca])) of cultured human cardiac fibroblasts were characterized in this study. In whole-cell configuration, depolarizing pulses evoked I (K(Ca)) in an outward rectification in these cells, the amplitude of which was suppressed by paxilline (1 microM: ) or iberiotoxin (200 nM: ). A large-conductance, Ca(2+)-activated K(+) (BK(Ca)) channel with single-channel conductance of 162 +/- 8 pS was also observed in human cardiac fibroblasts. Western blot analysis revealed the presence of alpha-subunit of BK(Ca) channels. The dynamic Luo-Rudy model was applied to predict cell behavior during direct electrical coupling of cardiomyocytes and cardiac fibroblasts. In the simulation, electrically coupled cardiac fibroblasts also exhibited action potential; however, they were electrically inert with no gap-junctional coupling. The simulation predicts that changes in gap junction coupling conductance can influence the configuration of cardiac action potential and cardiomyocyte excitability. I (k(Ca)) can be elicited by simulated action potential waveforms of cardiac fibroblasts when they are electrically coupled to cardiomyocytes. This study demonstrates that a BK(Ca) channel is functionally expressed in human cardiac fibroblasts. The activity of these BK(Ca) channels present in human cardiac fibroblasts may contribute to the functional activities of heart cells through transfer of electrical signals between these two cell types.

Parkinson’s disease (PD) is a neurodegenerative disease, which is associated with mitochondrial dysfunction and abnormal protein accumulation. No treatment can stop or slow PD. Autophagy inhibits neuronal death by removing damaged mitochondria and abnormal protein aggregations. Celastrol is a triterpene with antioxidant and anti-inflammatory effects. Up until now, no reports have shown that celastrol improves PD motor symptoms. In this study, we used PD cell and mouse models to evaluate the therapeutic efficacy and mechanism of celastrol. In the substantia nigra, we found lower levels of autophagic activity in patients with sporadic PD as compared to healthy controls. In neurons, celastrol enhances autophagy, autophagosome biogenesis (Beclin 1↑, Ambra1↑, Vps34↑, Atg7↑, Atg12↑, and LC3-II↑), and mitophagy (PINK1↑, DJ-1↑, and LRRK2↓), and these might be associated with MPAK signaling pathways. In the PD cell model, celastrol reduces MPP+-induced dopaminergic neuronal death, mitochondrial membrane depolarization, and ATP reduction. In the PD mouse model, celastrol suppresses motor symptoms and neurodegeneration in the substantia nigra and striatum and enhances mitophagy (PINK1↑ and DJ-1↑) in the striatum. Using MPP+ to induce mitochondrial damage in neurons, we found celastrol controls mitochondrial quality by sequestering impaired mitochondria into autophagosomes for degradation. This is the first report to show that celastrol exerts neuroprotection in PD by activating mitophagy to degrade impaired mitochondria and further inhibit dopaminergic neuronal apoptosis. Celastrol may help to prevent and treat PD.