The self-assembling behavior of synthetic amphiphiles is discussed. The bilayer membrane is formed spontaneously in water from a variety of dialkyl (C10-C20) amphiphiles with cationic, anionic, nonionic, and zwitterionic hydrophilic head groups. Appropriate triple-chain amphiphiles with rigid segments similarly produce the bilayer assembly. Two-headed, single-chain amphiphiles form the monolayer membrane. These results establish that the formation of molecular membranes is a general physicochemical phenomenon. The aggregate morphology (vesicle, lamella, tube, disk, etc) can be related to the molecular structure in the case of a group of the single-chain amphiphile. Physicochemical chracteristics (binding of biomolecules, phase transition and phase separation) of the synthetic bilayer are discussed.
The pacemaker activity of the S-A node cell was explained by reconstructing the pacemaker potential using a Hodgkin-Huxley type mathematical model which was based on the reported voltage clamp data. In this model four dynamic currents, the sodium current, iNa, the slow inward current, is, the potassium current, iK, and the hyperpolarizationactivated current, ih, in addition to a time-independent leak current, i1 were included. The model simulated the spontaneous action potential, the changes of activity induced by applying acetylcholine and epinephrine. It was strongly suggested that the pacemaker depolarization in the S-A node cell is mainly due to a gradual increase of is during diastole, and that the contribution of iK is much less compared to the current iK2 in the Purkinje fiber. The rising phase of the action potential was due to is and the plateau js determined by both the inactivation of is and activation of iK.
Acetylcholine induces both a fast conformational change of acetylcholine rece ptor that results in the opening of ion-conducting channels through the membrane, and a slow conformational change that results in an inactivation of the receptor (desensitization). The relationship between the binding of the agonist to the receptor and the receptor-mediated ion flux or the desensitization has been studied by three kinds of experiments; 1) ion flux measurements with a quench flow method, 2) fluorescence measurements with a stopped flow method and 3) α-toxin binding to the receptor. Several models are summarized and discussed.