Electrically induced gel-to-gel phase-transition in neurons Richard Kellermayer a,1 , Andrea Zsombok b,c,2 , Tibor Auer a , Ferenc Gallyas a,b, * a Department of Neurosurgery, Pe ´cs University, H-7623 Pe ´cs, Re ´t utca 2, Hungary b Clinical Neuroscience Research Group of the Hungarian Academy of Sciences at the Department of Neurosurgery, Pe ´cs University, H-7623 Pe ´cs, Re ´t utca 2, Hungary c Central Laboratory of Animal Research, Pe ´cs University, H-7624 Pe ´cs, Szigeti u ´t 12, Hungary Received 28 October 2005; accepted 1 November 2005 Abstract At the end of transcardial perfusions with ice-cold physiological saline for 30 min or with isoosmotic potassium chloride for 5 min, but im- mediately before perfusion fixation, condenser-discharge electric shocks were administered to rats through surface electrodes pressed onto the temporal muscles of the scalped skull. As a result, striking ultrastructural compaction came about in numerous neurons thinly scattered in certain brain areas. Its features displayed a high degree of similarity to those previously observed following the in vivo administration of the same kind of electric shocks. This surprising independence from the actual state of metabolism questions whether the ultrastructural compaction, induced either in vivo or post mortem, is the result of any cascade of enzyme-mediated processes. On the other hand, a physical mechanism, phase tran- sition propagated by non-covalent free energy stored in a cytoplasmic gel structure, which was proposed recently to explain a mechanically induced similar ultrastructural compaction, appears to apply also to the present case. Ó 2005 International Federation for Cell Biology. Published by Elsevier Ltd. All rights reserved. Keywords: Post-mortem experiments; ‘‘Dark’’ neurons; Ultrastructural compaction; Non-enzymatic mechanism; Stored non-covalent free energy 1. Introduction In connection with the physical state of the material filling all cytoplasmic spaces in eukaryotic cells that are not occupied by the ultrastructural components ‘‘visible’’ in the conventional transmission electron microscope (‘‘aqueous cytoplasm’’; Clegg, 1984) many conceptions between the extremes outlined below coexist in the relevant literature. The ‘‘dissolved-state’’ conception regards the aqueous cytoplasm as a concentrated solution in which the overwhelming majority of proteins, metabolites, inorganic ions and water molecules can diffuse freely. According to the ‘‘organized-state’’ conception, the overwhelming majority of the molecules of all these substances are bound by non-covalent interactions both to each other and also to the ‘‘visible’’ ultrastructural elements, forming a contin- uous gel-like structure throughout the cell. Although the organized-state conception has not been favored during recent decades, it has been supported by an abundance of observa- tions, partly from non-biological fields of research (referenced in Pollack, 2001). Among others, polymer chemistry has in- vented synthetic gels that can assume two or more metastable phases, each having a distinct free-energy minimum, a distinct set of macromolecular conformations and a distinct degree of water content (Annaka and Tanaka, 1992), and therefore a distinct volume. Initiated at a single point, transition from one gel phase to another can spread throughout the gel, pro- pelled by the difference in free energy (Tanaka et al., 1992). The initiation can be performed by a subtle change around * Corresponding author. Department of Neurosurgery, Pe ´cs University, H-7623 Pe ´cs, Re ´t utca 2, Hungary. Tel.: þ36 72 535930; fax: þ36 72 535931. E-mail addresses: richard.kellermayer@aok.pte.hu (R. Kellermayer), azsombok@mail1.vcu.edu (A. Zsombok), ferenc.gallyas.sen@aok.pte.hu (F. Gallyas). 1 Present address: Department of Medical Genetics and Developmental Medicine, Pe ´cs University, H-7623 Pe ´cs, Jo ´zsef A.u. 7, Hungary. 2 Present address: Department of Anatomy, Medical College of Virginia, Campus of Virginia Commonwealth University, Richmond, VA, USA. 1065-6995/$ - see front matter Ó 2005 International Federation for Cell Biology. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.cellbi.2005.11.002 Cell Biology International 30 (2006) 175e182 www.elsevier.com/locate/cellbi