The effects of r-aminobutyric acid(GABA) agonsits and antagonists were explored by the intracellular recording method to discern the preferential suppression of the ON component by GABA on the ON-OFF transient cell in the catfish (Ictalurus punctatus) retina. Experiments were performed in the superfused eyecup preparation. The animals were decapitated and pited before the eye, and the surrounding tissue was removed from the skull. The retina was exposed by excising the cornea, iris, and vitreous. This preparation rested on a wad of Ringer`s soaked cotton in contact with an Ag/Agcl reference electrode. Solutions were delivered through a manifold system that was connected to a pipette located near the absorbent wick. Electro-physiological recordings were made using standard intracellular electrodes filled with 2 M potassium acetate. The electrical signal was recorded with an amplifierand a penwriter, viewed on an oscilloscope, and stored on a data recorder. The light sources were red light-emitting-diode (LED) and the stimuli were full field illumination covering the cntire retina. GABA preferentially reduced ON light responses in ON-OFF transient cell. and GABA hyperpolarized bipolar cells, but the effects on ON bipolar cells were more sensitive than OFF bipolar cells. CACA and TACA, GABAc receptor agonist, did not act on bipolar cells. CACA and TACA, GABAc receptor agonists, hyperpolarized bipolar cells but the sensitivity deferences between ON and OFF bipolar cell were not observed. These results suggest that the preferential suppression of the ON component of the ON-OFF transient cell by GABA was resulted from the presynaptic mechanism that reduced bipolar cell input.
Animals ; Catfishes* ; Cornea ; Electrodes ; gamma-Aminobutyric Acid ; Iris ; Lighting ; Potassium Acetate ; Retina* ; Skull

The catfish (Ictalurus punctatus) retinal neurons were investigated by using the intracellular recording techniques to analyze the function of the chloride ions in the light responses and the ionic mechanisms of the depolarizing actions by GABA. Experiments were performed in the superfused retina-eyecup preparation. The retina was exposed by exicising the cornea, iris, and vitreous. A piece of absorbent tissue with a hole large enough to expose the retina was centered over the eyecup to serve as a wick to draw off the superfusate. Diffuse light stimuli were generated by light-emitting diode positioned above the eyecup. The recordings were made with the use of borosilicate glass micropipettes fashioned from' omega dot' capillary tubing filled with 2 M potassium acetate. Voltage recordings were obtained using an amplifier and amplified signals were recorded on a storage oscillocope, penwriter, and a data recorder. In the catfish retina, the dark membrane potentials were depolarized and the light evoked responses were enhanced in the chloride"-free medium on the catfish horizontal cells. The amplitude of the light evoked potentials were increased by chloride free Ringer's solution on the ON- and OFF-bipolar cells. But the dark membrane potentials were hyperpolarized on the ON-bipolar cell and depolarized on the OFF-bipolar cells in the chloride free medium. The chloride free Ringer's solution changed the light response from ON-sustained to OFF-sustained without any change in amplitude on the ON-sustained cell. The depolarizing actions by GABA on the horizontal cells were maintained in chloride-free environment. But GABA did not abolished the light evoked potentials of the horizontal cell and the ON-sustained cell under the chloride free environment. The results suggest that chloride ion has important roles on the signal transmission of the dark periods in the catfish retina and the depolarizing actions by GABA on the neurons in the catfish retina might be chloride dependent.
Capillary Tubing ; Catfishes* ; Cornea ; Evoked Potentials ; gamma-Aminobutyric Acid ; Glass ; Ions* ; Iris ; Membrane Potentials ; Neurons ; Potassium Acetate ; Receptors, GABA ; Retina ; Retinal Neurons* ; Retinaldehyde*

The effect of protein kinase C (PKC) signaling pathway on the activity of voltage-dependent delayed rectifier potassium channel (K(V)) and the expression of K(V) isoform K(V)1.5 in rat bronchial smooth cells (BSMCs) were investigated with whole-cell patch clamp, Western-blot and RT-PCR techniques. The results showed: (1) phorbol 12-myristate 13-acetate (PMA), a PKC activator, caused a significant inhibition of K(V) channel currents in rat BSMCs. The inhibition was partly abolished by Ro31-8220, a PKC inhibitor. (2) PMA caused a significant suppression of the expression of K(V)1.5 mRNA and protein in rat BSMCs. These effects were attenuated by Ro31-8220. The results suggest that in rat BSMCs PKC activation inhibits K(V) currents and down-regulates the expression of K(V)1.5.
Animals ; Bronchi ; cytology ; Cells, Cultured ; Female ; Indoles ; pharmacology ; Kv1.5 Potassium Channel ; genetics ; physiology ; Male ; Membrane Potentials ; physiology ; Myocytes, Smooth Muscle ; cytology ; physiology ; Patch-Clamp Techniques ; Protein Kinase C ; metabolism ; physiology ; RNA, Messenger ; genetics ; metabolism ; Rats ; Rats, Sprague-Dawley ; Tetradecanoylphorbol Acetate ; pharmacology

CG200745 is a novel inhibitor of histone deacetylases (HDACs), initially developed for treatment of various hematological and solid cancers. Because it is water-soluble, it can be administered orally. We hypothesized that the HDAC inhibitor, CG200745, attenuates cardiac hypertrophy and fibrosis in deoxycorticosterone acetate (DOCA)-induced hypertensive rats. For establishment of hypertension, 40 mg/kg of DOCA was subcutaneously injected four times weekly into Sprague-Dawley rats. All the rats used in this study including those in the sham group had been unilaterally nephrectomized and allowed free access to drinking water containing 1% NaCl. Systolic blood pressure was measured by the tail-cuff method. Blood chemistry including sodium, potassium, glucose, triglyceride, and cholesterol levels was analyzed. Sections of the heart were visualized after trichrome and hematoxylin and eosin stain. The expression of hypertrophic genes such as atrial natriuretic peptide A (Nppa) and atrial natriuretic peptide B (Nppb) in addition to fibrotic genes such as Collagen-1, Collagen-3, connective tissue growth factor (Ctgf), and Fibronectin were measured by quantitative real-time PCR (qRT-PCR). Injection of DOCA increased systolic blood pressure, heart weight, and cardiac fibrosis, which was attenuated by CG200745. Neither DOCA nor CG200745 affected body weight, vascular contraction and relaxation responses, and blood chemistry. Injection of DOCA increased expression of both hypertrophic and fibrotic genes, which was abrogated by CG200745. These results indicate that CG200745 attenuates cardiac hypertrophy and fibrosis in DOCA-induced hypertensive rats.
Animals ; Blood Pressure ; Body Weight ; Cardiomegaly* ; Chemistry ; Cholesterol ; Connective Tissue Growth Factor ; Desoxycorticosterone ; Desoxycorticosterone Acetate ; Drinking Water ; Eosine Yellowish-(YS) ; Fibronectins ; Fibrosis* ; Glucose ; Heart ; Hematoxylin ; Histone Deacetylase Inhibitors* ; Histone Deacetylases* ; Histones* ; Hypertension ; Methods ; Potassium ; Rats* ; Rats, Sprague-Dawley ; Real-Time Polymerase Chain Reaction ; Relaxation ; Sodium ; Triglycerides