Interactions of chloride and amiloride with the renal Na+/H/ antiporter

Amiloride is a reversible inhibitor of the Na+/H+ antiporter which acts at the external aspect of the transport system. The kinetics of inhibition of the Na+/H+ antiporter with amiloride have been controversial, with the usual finding of simple competitive inhibition, but with other reports of mixed and noncompetitive inhibition of the transporter by amiloride. The present experiments demonstrate that the chloride content of the external transport buffer affects the kinetics of amiloride inhibition. Either simple competitive or mixed inhibition by amiloride was observed in the same vesicle preparations depending on the presence of chloride or gluconate in the buffer. The effect of chloride on the inhibitory effect of amiloride was dependent on the concentration of chloride and amiloride. Similar effects were observed with more potent analogues of amiloride. These findings suggest that the external aspect of the antiporter has a site or sites at which the inhibitory effects of amiloride on the Na+/H+ antiporter can be modified by chloride, even though chloride has only slight effects on the kinetics of the Na+/H+ antiporter in the absence of amiloride.     

Physiology based simulation model of triangle shape recognition

The present paper considers the relation between the shape of a triangle and probability of its recognition. An effect of triangle size on perception of its shape is examined in the first experiment. In the second the loci of eye fixations during triangle recognition task are recorded and analysed. A simulation model of the recognition process is proposed. The model is based on two main assumptions: 1. an accuracy of shape processing is related to the cortical magnification factor, 2. a subject's response depends on actual position of eye fixation. The validity of the model is verified by comparing the theoretical and experimental response distributions. Some psychophysiological implications are then discussed.A partial report of this research was given at the Annual Meeting of the Association for Research in Vision and Ophthalmology (Pizlo and Gradus-Pizlo 1986)     

Blockage of tropoelastin secretion by monensin represses tropoelastin synthesis at a pretranslational level in rat smooth muscle cells.

The blockage of protein secretion in the R22 cultured rat aortic smooth muscle cell strain with monensin repressed tropoelastin gene expression at the mRNA level by ca. 50-fold as measured by biosynthetic pulse-labeling, in vitro translation, and hybridization with a tropoelastin genomic DNA probe. These results suggest that tropoelastin gene expression is autoregulated, and they represent the first reported effect of monensin on gene expression.     

A comparative analysis of photosynthetic characteristics of hulless barley at two altitudes on the Tibetan Plateau

To determine the photosynthetic characteristics of C₃ plants and their sensitivity to CO₂ at different altitudes on the Tibetan Plateau, hulless barley (Hordeum vulgare L. ssp. vulgare) was grown at altitudes of 4,333 m and 3,688 m. Using gas-exchange measurements, photosynthetic parameters were simulated, including the maximum net photosynthesis (P _max) and the apparent quantum efficiency (α). Plants growing at higher altitude had higher net photosynthetic rates (P _N), photosynthesis parameters (P _max and α) and sensitivities to CO₂ enhancement than plants growing at lower altitude on the Tibetan Plateau. The enhancements of P _N, P _max, and α for plants growing at higher altitude, corresponding with 10 μmol(CO₂) mol⁻¹ increments, were approximately 0.20∼0.45%, 0.05∼0.20% and 0.12∼0.36% greater, respectively, than for plants growing at lower altitude, respectively, where CO₂ levels rose from 10 to 170 μmol(CO₂) mol⁻¹. Therefore, on the Tibetan Plateau, the changes in the photosynthetic capacities and the photosynthetic sensitivities to CO₂ observed in the C₃ plants grown above 3,688 m are likely to increase with altitude despite the decreasing CO₂ partial pressure.