Conductances and Selective Permeability of Connexin43 Gap Junction Channels Examined in Neonatal Rat Heart Cells

• Published in: Circulation research 1997-05, Vol.80 (5), p.708-719
• Main Authors: Valiunas, Virginijus, Bukauskas, Feliksas F, Weingart, Robert
• Format: Article
• Language: English
• Subjects: Animals; Animals, Newborn; Arachidonic Acid - pharmacology; Biological and medical sciences; Cell physiology; Cells, Cultured; Connexin 43 - physiology; Cytochrome P-450 Enzyme System - pharmacology; Fundamental and applied biological sciences. Psychology; Gap Junctions - drug effects; Gap Junctions - physiology; Ion Channel Gating - drug effects; Ion Channels - drug effects; Ion Channels - physiology; Microscopy; Molecular and cellular biology; Muscle contraction; Myocardium - cytology; Permeability; Rats; Rats, Wistar; Uncoupling Agents - pharmacology
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.80.5.708

Myocytes from neonatal rat hearts were used to assess the conductive properties of gap junction channels by means of the dual voltage-clamp method. The experiments were carried out on three types (groups) of preparations(1) induced cell pairs, (2) preformed cell pairs with few gap junction channels (1 to 3 channels), and (3) preformed cell pairs with many channels (100 to 200 channels) after treatment with uncoupling agents such as SKF-525A (75 micro mol/L), heptanol (3 mmol/L), and arachidonic acid (100 micro mol/L). In group 1, the first opening of a newly formed channel was slow (20 to 65 ms) and occurred 7 to 25 minutes after physical cell contact. The rate of channel insertion was 1.3 channels/min. Associated with a junctional voltage gradient (Vj), the channels revealed multiple conductances, a main open state [gammaj(main state)], several substates [gammaj(substates)], and a residual state [gammaj(residual state)]. On rare occasions, the channels closed completely. The same phenomena were observed in groups 2 and 3. The existence of gammaj(residual state) provides an explanation for the incomplete inactivation of the junctional current (Ij) at large values of Vj in cell pairs with many gap junction channels. The values of gammaj(main state) and gammaj(residual state) gained from groups 1, 2, and 3 turned out to be comparable and hence were pooled. The fit of the data to a Gaussian distribution revealed a narrow single peak for both conductances. The values of gammaj were dependent on the composition of the pipette solution. Solutions were as follows(1) KCl solution, gammaj(main state)=96 pS and gammaj(residual state)=23 pS; (2) Cs sup + aspartate sup - solution, gammaj(main state)=61 pS and gammaj(residual state)=12 pS; and (3) tetraethylammonium sup + aspartate sup - solution, gammaj(main state)=19 pS and gammaj(residual state)=3 pS. The respective gammaj(main state)-to-gamma sub j(residual state) ratios were 4.2, 5.1, and 6.3. This indicates that the residual state restricts ion permeation more efficiently than does the main state. Transitions of Ij between open states (main open state, substates, and residual state) were fast (