Biomedical subjects

H Qian

Publications and source records attributed to H Qian.

183 records · Page 11Linked to original sources

PubMedDate not supplied

Gap-junctional properties of electrically coupled skate horizontal cells in culture.

Whole-cell voltage-clamp recordings were used to examine the unusual pharmacological properties of the electrical coupling between rod-driven horizontal cells in skate retina as revealed previously by receptive-field measurements (Qian & Ripps, 1992). The junctional resistance was measured in electrically coupled cell pairs that had been enzymatically isolated and maintained in culture; the typical value was about 19.92 M omega (n = 45), more than an order of magnitude lower than the nonjunctional membrane resistance. These data and the intercellular spread of the fluorescent dye Lucifer Yellow provide a good indication that skate horizontal cells are well coupled. The junctional conductance between cells was not modulated by the neurotransmitters dopamine (200 microM) or GABA (1 mM), nor was it affected by the membrane-permeable analogues of cAMP or cGMP, or the adenylate cyclase activator, forskolin. Although resistant to agents that have been reported to alter horizontal-cell coupling in cone-driven horizontal cells, the junctional conductance between paired horizontal cells of skate was greatly reduced by the application of 20 mM acetate, which is known to effectively reduce intracellular pH. Together with the results obtained in situ on the receptive-field properties of skate horizontal cells, these findings indicate that the gap-junctional properties of rod-driven horizontal cells of the skate are fundamentally different from those of cone-driven horizontal cells in other species. This raises the possibility that there is more than one class of electrical synapse on vertebrate horizontal cells.

Animals↗

PubMedDate not supplied

A comparison of GABAC and rho subunit receptors from the white perch retina.

There is increasing evidence that GABAC receptors are composed of GABA rho subunits. In this study, we compared the properties of native GABAC receptors with those of receptors composed of a GABA rho subunit. A homologue of the GABA rho gene was cloned from a white perch (Roccus americana) retinal cDNA library. The clone (perch-s) has an open reading frame of 1422 nucleotide base pairs and encodes a predicted protein of 473 amino acids. It is highly homologous to GABA rho subunits cloned from human and rat retinas. The receptors (perch-s receptor) expressed by this gene in Xenopus oocytes show properties similar to those of the GABAC receptors present on white perch retinal neurons. GABA induced a sustained response that had a reversal potential of -27.1 +/- 3.6 mV. The EC50 for the response was 1.74 +/- 1.25 microM, a value similar to that reported for GABAC receptors. Pharmacologically, the responses were bicuculline insensitive and not modulated by either diazepam or pentobarbital as is the case for GABAC receptors. There were, however, some distinct differences between native GABAC and perch-s receptors. I4AA acts as a partial agonist on perch-s receptors whereas it is strictly an antagonist on native GABAC receptors. Picrotoxin inhibition is noncompetitive on perch-s receptors, but both competitive and noncompetitive on GABAC receptors. We conclude that GABAC receptors are formed by GABA rho subunits but that native GABAC receptors probably consist of a mixture of GABA rho subunits.

Amino Acid Sequence↗

PubMedDate not supplied

Effects of callus and bonding on strains in bone surrounding an implant under bending.

Descriptions of the healing and adaptation of endosseous implants have been provided; however, their effects on mechanical parameters such as maximum and minimum principal strains, strain energy density, and maximum shear strain have not been addressed. Three linear, elastic, and partially anisotropic finite element models were generated to simulate the immediate postoperative period, time of provisional loading, and long-term adaptation of bone surrounding implants. In each model, unbonded and bonded interface conditions were imposed. Bone geometry was estimated from dental implants placed in femurs of hounds. A lateral load was applied and the mechanical parameters were calculated. Interface bonding decreased the peak minimum principal strain 2.6 to 6.4 fold, while the presence of a callus reduced it 3 to 7 fold. These data document the critical stabilizing roles of callus and bond formation.

Animals↗