Selectivity of Connexin-Specific Gap Junctions Does Not Correlate With Channel Conductance

• Published in: Circulation research 1995-12, Vol.77 (6), p.1156-1165
• Main Authors: Veenstra, Richard D, Wang, Hong-Zang, Beblo, Dolores A, Chilton, Mark G, Harris, Andrew L, Beyer, Eric C, Brink, Peter R
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Blotting, Northern; Cell membranes. Ionic channels. Membrane pores; Cell structures and functions; Cells, Cultured; Chickens; Connexins - genetics; Connexins - metabolism; Diffusion; Electric Conductivity; Electrophysiology; Fluoresceins; Fluorescent Dyes; Fundamental and applied biological sciences. Psychology; Gap Junctions - metabolism; Gap Junctions - physiology; Genetic Vectors; Humans; Ion Channels - genetics; Ion Channels - metabolism; Ion Channels - physiology; Liposomes; Mice; Models, Anatomic; Models, Biological; Molecular and cellular biology; Molecular Weight; Neuroblastoma; Patch-Clamp Techniques; Phosphatidylethanolamines; Plasmids - genetics; Rats; Second Messenger Systems; Surface Properties; Transfection
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.77.6.1156

Connexins form a variety of gap junction channels that vary in their developmental and tissue-specific levels of expression, modulation of gating by transjunctional voltage and posttranslational modification, and unitary channel conductance (gamma sub j). Despite a 10-fold variation in gammaj, whether connexinspecific channels possess distinct ionic and molecular permeabilities is presently unknown. A major assumption of the conventional model for a gap junction channel pore is that gamma sub j is determined primarily by pore diameter. Hence, molecular size permeability limits should increase and ionic selectivity should decrease with increasing channel gammaj (and pore diameter). Equimolar ion substitution of 120 mmol/L KCl for potassium glutamate was used to determine the unitary conductance ratios for rat connexin40 and connexin43, chicken connexin43 and connexin45, and human connexin37 channels functionally expressed in communication-deficient mouse neuroblastoma (N2A) cells. Comparison of experimental and predicted conductance ratios based on the aqueous mobilities of all ions according to the Goldman-Hodgkin-Katz current equation was used to determine relative anion-to-cation permeability ratios. Direct correlation of junctional conductance with dye transfer of two fluorescein-derivatives (2 mmol/L 6-carboxyfluorescein or 2 prime,7 prime-dichlorofluorescein) was also performed. Both approaches revealed a range of selectivities and permeabilities for all five different connexins that was independent of channel conductance. These results are not consistent with the conventional simple aqueous pore model of a gap junction channel and suggest a new model for connexin channel conductance and permselectivity based on electrostatic interactions. Divergent conductance and permeability properties are features of other classes of ion channels (eg, Na and K channels), implying similar mechanisms for selectivity.(Circ Res. 1995;77:1156-1165.)