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Increased availability and open probability of single L-type calcium channels from failing compared with nonfailing
F Schröder1, R Handrock, D J Beuckelmann
1Department of Pharmacology, University of Cologne, Germany.
Insights
In human heart failure, individual L-type calcium channels show altered properties, impacting cardiac function. This study reveals changes in channel availability and open probability in failing hearts.
Area of Science:
- Cardiology
- Molecular Biology
- Physiology
Background:
- The precise role of L-type calcium channels in human heart failure remains incompletely understood, particularly based on prior whole-cell recording studies.
- Investigating these channels is crucial for understanding cardiac dysfunction in heart failure.
Purpose of the Study:
- To investigate the functional properties of L-type calcium channels in human heart failure.
- To determine if alterations in channel kinetics or expression contribute to the pathophysiology of heart failure.
Main Methods:
- Utilized single-channel recording techniques on left ventricular myocytes from nonfailing donor hearts and hearts with dilated or ischemic cardiomyopathy.
- Measured peak average currents, channel availability, and open probability.
- Assessed the effects of cAMP-dependent stimulation and phosphatase inhibition (okadaic acid).
- Quantified the expression of calcium channel alpha1c- and beta-subunits using Northern blot analysis.
Main Results:
- Peak average currents of L-type calcium channels were significantly enhanced in failing hearts compared to nonfailing controls.
- This enhancement was attributed to increased channel availability and open probability in heart failure.
- Channels from failing hearts exhibited prolonged availability, suggesting a dephosphorylation defect.
- No significant alterations were found in the expression of alpha1c- and beta-subunits, and whole-cell current density was not increased.
Conclusions:
- Individual L-type calcium channels are fundamentally altered in severe human heart failure.
- These alterations likely contribute to the impairment of cardiac excitation-contraction coupling in heart failure.
- Findings suggest a potential defect in channel dephosphorylation as a mechanism for altered channel function.
Background:
The role of the L-type calcium channel in human heart failure is unclear, on the basis of previous whole-cell recordings.
Methods And Results:
We investigated the properties of L-type calcium channels in left ventricular myocytes isolated from nonfailing donor hearts (n= 16 cells) or failing hearts of transplant recipients with dilated (n=9) or ischemic (n=7) cardiomyopathy. The single-channel recording technique was used (70 mmol/L Ba2+). Peak average currents were significantly enhanced in heart failure (38.2+/-9.3 fA) versus nonfailing control hearts (13.2+/-4.5 fA, P=0.02) because of an elevation of channel availability (55.9+/-6.7% versus 26.4+/-5.3%, P=0.001) and open probability within active sweeps (7.36+/-1.51% versus 3.18+/-1.33%, P=0.04). These differences closely resembled the effects of a cAMP-dependent stimulation with 8-Br-cAMP (n= 11). Kinetic analysis of the slow gating shows that channels from failing hearts remain available for a longer time, suggesting a defect in the dephosphorylation. Indeed, the phosphatase inhibitor okadaic acid was unable to stimulate channel activity in myocytes from failing hearts (n=5). Expression of calcium channel subunits was measured by Northern blot analysis. Expression of alpha1c- and beta-subunits was unaltered. Whole-cell current measurements did not reveal an increase of current density in heart failure.
Conclusions:
Individual L-type calcium channels are fundamentally affected in severe human heart failure. This is probably important for the impairment of cardiac excitation-contraction coupling.