A cyclic-AMP-gated conductance in cochlear hair cells

AbstractThe patch clamp technique was used to record cAMP-dependent currents of the guinea pig cochlear hair cell plasma membrane. Data obtained indicate that the channels passing this current are moderately selective for monovalent cations and are effectively blocked by L-cis-diltiazem and reversibly blocked by 1 mM Mg2+ or Ca2+. The single-channel unit conductance estimated in the absence of divalent cations is about 16 pS. The results demonstrate that cyclic nucleotide-dependent channels of cochlear hair cells are virtually identical to the photoreceptor and olfactory ones

L-arginine supplementation protects exercise performance and structural integrity of muscle fibers after a single bout of eccentric exercise in rats.

Eccentric exercise is known to disrupt sarcolemmal integrity and induce damage of skeletal muscle fibers. We hypothesized that L-arginine (L-Arg; nitric oxide synthase (NOS) substrate) supplementation prior to a single bout of eccentric exercise would diminish exercise-induced damage. In addition, we used N-nitro-L-arginine methyl ester hydrochloride (L-NAME; NOS inhibitor) to clarify the role of native NOS activity in the development of exercise-induced muscle damage. Rats were divided into four groups: non-treated control (C), downhill running with (RA) or without (R) L-Arg supplementation and downhill running with L-NAME supplementation (RN). Twenty four hours following eccentric exercise seven rats in each group were sacrificed and soleus muscles were dissected and frozen for further analysis. The remaining seven rats in each group were subjected to the exercise performance test. Our experiments showed that L-Arg supplementation prior to a single bout of eccentric exercise improved subsequent exercise performance capacity tests in RA rats when compared with R, RN and C rats by 37%, 27% and 13%, respectively. This outcome is mediated by L-Arg protection against post-exercise damage of sarcolemma (2.26- and 0.87-fold less than R and RN groups, respectively), reduced numbers of damaged muscle fibers indicated by the reduced loss of desmin content in the muscle (15% and 25% less than R and RN groups, respectively), and diminished µ-calpain mRNA up-regulation (42% and 30% less than R and RN groups, respectively). In conclusion, our study indicates that L-Arg supplementation prior to a single bout of eccentric exercise alleviates muscle fiber damage and preserves exercise performance capacity

Exercise performance capacity of C, R, RA and RN rats twenty four hours post a single bout of eccentric exercise.

<p>N = 7. *indicates a significant difference from control, p<0.05; #indicates a significant difference from RA, p<0.05. This Figure was previously published as proceedings in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094448#pone.0094448-Lomonosova2" target="_blank">[67]</a>.</p

Representative picture of the typical EPR spectrum of sample from rat soleus muscle recorded after Fe-DETC administration.

<p>a, a representative spectrum from soleus muscle of rat from CA group after 48 hours of L-Arg administration with drinking water; b, a representative spectrum from soleus muscle of control rat without L-Arg administration. The spectrum component used to evaluate relative NO concentration is indicated by the arrow.</p

Representative picture of the immunostaining of samples from soleus muscles of C and R rats with antibodies against dystrophin (A) and proportion of muscle fibers with disruptions of immunostaining in the dystrophin layer (B) after normalization for the total number of fibers in each sample.

<p>Arrows in A indicate disruptions of immunostaining in the dystrophin layer. N = 7. *indicates a significant difference from control, p<0.05; #indicates a significant difference from RA, p<0.05.</p

Representative picture of the preliminary evaluations of antibodies (A) and Western blotting of samples from soleus muscles of C, R, RA and RN rats with antibodies against desmin and GAPDH (B), and relative desmin protein expression level (C) after normalization for the GAPDH protein expression level in each sample.

<p>N = 7. *indicates a significant difference from control, p<0.05; #indicates a significant difference from RA, p<0.05. This Figure was previously published as proceedings in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094448#pone.0094448-Lomonosova2" target="_blank">[67]</a>.</p

Evaluation of gene expression in soleus muscles of C, R, RA and RN rats.

<p>mRNA expression of genes involved in NO generation, protein degradation and cytoprotection was evaluated by quantitative PCR analysis. N = 7. Values are normalized to the expression of β-actin in each sample. *indicates a significant difference from control, p<0.05; #indicates a significant difference from RA, p<0.05.</p

Primers used for QRT-PCR study.

<p>Primers used for QRT-PCR study.</p