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Cell coupling between ventricular myocyte pairs from connexin43-deficient murine hearts
Jian-An Yao1, David E Gutstein, Fangyu Liu
1Department of Pharmacology and Center for Molecular Therapeutics, College of Physicians and Surgeons, Columbia University, 630 W 168th St, New York, NY 10032, USA.
Abstract:
Mice with cardiac-restricted inactivation of the connexin43 gene (CKO mice) have moderate slowing of ventricular conduction and lethal arrhythmias. Mechanisms through which propagation is maintained in the absence of Cx43 are unknown. We evaluated gap junctional conductance in CKO ventricular pairs using dual patch clamp methods. Junctional coupling was reduced to 4+/-2 nS (side-to-side) and 11+/-2 nS (end-to-end), including 21% of cell-pairs with no detectable coupling, compared with 588+/-104 nS (side-to-side) and 558+/-92 nS (end-to-end) in control cell-pairs. Voltage dependence of control gap junctions was characteristic of Cx43. CKO conductance showed increased voltage dependence, suggesting low-level expression of other connexin isoforms. From theoretical models, this degree of CKO coupling is not expected to support levels of conduction persisting in vivo, suggesting the possibility that there are additional mechanisms for maintained propagation when gap junctional conductance is severely reduced.
Insights
Cardiac connexin43 gene inactivation in mice slows ventricular conduction and causes arrhythmias. Severely reduced gap junctional coupling suggests other mechanisms maintain propagation, warranting further investigation.
Area of Science:
- Cardiovascular physiology
- Molecular cardiology
- Biophysics
Background:
- Connexin43 (Cx43) is crucial for cardiac electrical conduction.
- Cardiac-restricted inactivation of Cx43 (CKO mice) leads to ventricular conduction slowing and lethal arrhythmias.
- The mechanisms maintaining cardiac propagation in the absence of Cx43 are not fully understood.
Purpose of the Study:
- To investigate the residual gap junctional coupling in CKO mouse ventricular myocytes.
- To determine if the observed coupling levels can account for in vivo ventricular conduction.
- To explore potential alternative mechanisms for cardiac impulse propagation.
Main Methods:
- Dual patch clamp recordings from isolated ventricular myocyte pairs in CKO and control mice.
- Quantification of side-to-side and end-to-end junctional conductance.
- Analysis of voltage dependence of gap junction currents.
- Theoretical modeling to assess the sufficiency of measured coupling for in vivo conduction.
Main Results:
- Junctional coupling in CKO ventricular pairs was drastically reduced (4-11 nS) compared to controls (558-588 nS).
- A significant percentage (21%) of CKO cell pairs exhibited no detectable coupling.
- CKO gap junction conductance showed increased voltage dependence, suggesting low-level expression of other connexin isoforms.
- Theoretical models indicated that the measured CKO coupling is insufficient to support the observed in vivo conduction levels.
Conclusions:
- Cardiac-restricted inactivation of connexin43 severely impairs ventricular myocyte gap junctional coupling.
- Residual coupling in CKO mice is insufficient to explain the observed ventricular conduction in vivo.
- Alternative mechanisms likely contribute to maintaining cardiac impulse propagation when connexin43-mediated gap junctional conductance is significantly reduced.