Session A-3
11:30 - 12:30

11:30 - 12:00 : Srinivasan, Parthasarathy (Mathematics, Cleveland State University)
-Title: Estimating Biophysical Properties of Nitric Oxide
Nitric oxide (NO) derived from the endothelium is a potent vasodilator, and plays a crucial role in maintaining vascular tone. Being a small diatomic molecule, it has so far been assumed that the diffusion rate of NO is the same as in solution. However, this hypothesis has not been tested experimentally. Recent methods have enabled us to measure the flux of NO across the aortic wall directly. We present a simple mathematical model from which we can obtain the diffusion and partition coefficients of NO across the aortic wall using these measurements. Our results show that the diffusion coefficient of NO in tissues is four times slower than in solution under normal physiological conditions, which indicates that the diffusion of NO (and hence its bioavailability) in the vascular wall is crucially dependent on the environment where the molecule diffuses. We also examine the role that oxygen plays in the bioavailability of NO in the vasculature. Our results suggest that the oxygen-dependent NO consumption could play an important role in dilating blood vessels during hypoxia by increasing the effective NO diffusion distance.

12:00 - 12:30 : Kang, Yeona (Materials Science & Engineering, SUNY at Stony Brook)
-Authors: Yeona Kang(*) and C. M. Fortmann
-Title: A structural basis for the Hodgkin and Huxley relation
Neural channel transport was analyzed using a previously reported relation for charged particle transport in two energy-type gradients: the electric field and here a water/strucural deformation energy. Neural channels are lined with alpha-helix structures filled with water vapor and sequestered hydrophobic amino acids arranged to present minimum water vapor and water-hydrophobic interface. Cation point charges generate enormous electric fields on sub-nanometer distances. Electrostatic energy reduction is characterized by dielectric water being pulled toward the transporting ion deforming the neural channel. An ion-water-structure coupling energy is induced by changes in channel diameter width. The resultant two energy gradient relation for cation transport: reduces to the Hodgkin-Huxley relation [A. L. Hodgkin and A. F. Huxley, J. Physiol. (London) 116, 449 (1952)], explains channel selectivity and environmental sensitivity, predicts fast non-dispersive transport under a narrow range of conditions, and produces current-voltage characteristics consistent with observation.