Abstract 15810: Direct Evidence of Functional Coupling of β2 Adrenergic Receptors With L-type Calcium Channels in Rat Cardiomyocytes and its Loss in Heart Failure
Introduction: L-type calcium channels (LTCCs) are crucially involved in excitation-contraction coupling. β1 and β2 adrenergic receptors (βARs) are important mediators of LTCC function via production of the second messenger cAMP. Stimulation of LTCCs through β2AR happens only in the close proximity of the channel suggesting a coupling between LTCC with β2AR rather than with β1AR. We wanted to find out if this coupling is exclusive of the channels located in the t-tubules (TTs) or it can be found in other areas of cell plasma membranes (crests). We also wanted to look at failing cardiomyocytes and see if the coupling is impaired.
Method: We applied super-resolution scanning patch-clamp to record functional LTCCs from control and 16-weeks post-MI heart failure rat ventricular cardiomyocytes. Stimulation of β1AR (ISO 1.0μM + ICI 50nM) or β2AR (ISO 1.0μM + CGP 0.3μM), on specific microdomains (TTs or crests) was applied locally though the pipette (350nm tip diameter) in cell-attached mode.
Results: In control cells, local stimulation of β2AR increased the occurrence (from 30% to 50% on TTs and from 13% to 27% on crests) and the open probability of LTCCs (0.045±0.007 vs. 0.066±0.007 on TTs, p<0.05 and 0.026±0.008 vs 0.046±0.002 on crest, p<0.05). Surprisingly, local stimulation of β1AR did not increase neither occurrence nor open probability of LTCC both in the TTs and in the crests. In failing cells, a microdomain-specific disruption of signalling was observed, with β2AR stimulation only increasing the occurrence (from 33% to 56%) and the open probability (0.079±0.011 vs 0.0107±0.009, p<0.05) of LTCCs in the crests but not in the TTs.
Conclusions: This study provides first direct evidence of the specific coupling of β2ARs with LTCCs that is also dependent on the location and is disrupted in failing cardiomyocytes.
Author Disclosures: J.L. Sanchez-Alonso: None. J. Gorelik: None.
- © 2015 by American Heart Association, Inc.