No abstract

Incorporated terbium, Tb3+, activates the Ca‐activated K channel found in the resealed erythrocyte ghost membrane and allows the net efflux of K. As in the case of Ca activation, low levels of external K stimulate the net efflux of K. The action of incorporated Tb3+ seems to be analogous to that of incorporated Ca. Externally applied Tb3+, however, inhibits the net efflux of K after either Ca or Tb3+ activation. The net‐efflux of K can be inhibited by Tb3+ even after partial digestion of the channel by low levels of incorporated trypsin. Furthermore, the channel when incorporated into planar bilayers, can be inhibited by Tb3+. Externally applied Tb3+ does not seem to inhibit net K efflux indirectly via inhibition of the pathways for the co‐transported anions. In addition because of the low concentrations of Tb3+ required for inhibition, it seems unlikely that an alteration of surface potential is responsible for the observed effects.

The transport properties of the Ca-activated, K channel in the resealed human red blood cell ghost can be modified by the action of incorporated trypsin. Membranes were maximally depleted of diffusible cytoplasmic components by hemolysis on a gel filtration column at 0 "C. Subsequently, isotonicity was restorted and 0.01 -1 pg/ml trypsin incorporated. Partial digestion of the membrane proteins occurred during resealing. As the degree of tryptic digestion increased, the channel became initially permeable to K and later to both K and Na; and then the channel became refractory to the action of applied Ca. The observations suggest that tryptic digestion of proteins at the inner membrane surface leads to modifications of the selectivity filter and the Ca-receptor site of the channel. The modifications probably stem from alterations at the inner surface of a transmembrane protein which acts as a channel. Under conditions where selectivity is lost, the channel is still inhibited by externally applied TbCl,.

No abstract

Regeneration of damaged neurons has been one of the main challenges in the attempt to cure brain damages occur from neurodegenerative diseases and head injuries. Successful formation of functional synapses on artificial substrates is a very important step in the development of engineered in vitro neural networks. We have recently shown that spherical supported bilayer lipid membranes (SS-BLMs) can be used as a novel substrate to achieve presynaptic accumulation at an in vitro synaptic junction. 1 The results indicate that lipid membrane domains may play a role in the observed phenomenon, in addition to the chemical and electrostatic interactions between the neurons and SS-BLMs. 2 With the help of domain specific fluorescent dyes, micron-sized lipid phase domains were specifically labeled on Giant Unilamellar Vesicles (GUVs) and on silica beads. Experiments, in vitro, clearly show that specific membrane domains play a role in the synapse formation. These results as well as Cryo-TEM based molecular level confirmation of presynapse formation on artificial substrates will be presented.The aspect of lipid membrane domains in synapse formation is key in developing many neuroengineering approaches to design functional artificial synapse formation as well as for synaptogenesis studies in vivo.