Abstract 13390: Beat-to beat increases in Calcium Induced Calcium Release May be Mediated by Rapidly Enhanced Phosphorylation During Selective β1-Adrenergic Stimulation in Rat Ventricle
Introduction: CICR is influenced by ICa amplitude and the phosphorylation status of proteins associated with ECC e.g. RyR2, PLB and indeed the L-type Ca2+ channels themselves. However, the specific contribution of these parameters has not been fully established. We therefore investigated the interaction between short term (2 sec) β-adrenergic stimulation and/or high [Ca2+]o,and CICR.
Methods: Fura-2 loaded, voltage clamped myocytes were depolarised from -40 to 0 mV (0.5 Hz, n=6-12) in the absence or presence of the test substance. A train of conditioning pulses prior to the test pulse was used to standardise SR Ca2+ load. A TTL-controlled solution changer was used to change extracellular solutions to 5.0 mM [Ca2+]o or 1.0 μM isoprenaline, either alone or simultaneously. ICI 118,551 selectively blocked ß2 adrenoceptor.
Results: During steady-state stimulation, elevation of [Ca2+]o from 1.0 to 5.0 mM increased ICa by 37 ± 9 % and [Ca2+]i transient by 64 ± 11 %, (P<0.01). Isoprenaline alone also increased both ICa and [Ca2+]i transient by 68±8 % and 52±10 %, respectively (P<0.001). When isoprenaline and 5.0 mM [Ca2+]o were applied simultaneously, both ICa and [Ca2+]i transient amplitudes increased to a much greater extent (122 ± 14% and 104±39 %, respectively P<0.05). However, during beat-to-beat measurements, exposure to the rapid application of 5.0 mM [Ca2+]o alone increased ICa amplitude by 36±6% (P<0.001) but had no significant effect on the [Ca2+]i transient amplitude (5±5%). Similarly, rapid application of isoprenaline alone produced only a small increase in ICa amplitude (9±1 %, (P<0.005) but again with little or no change in [Ca2+]i (1±1%) However, the simultaneous and rapid application of both 5.0 mM [Ca2+]o and isoprenaline produced effects on CICR that were much greater: ICa increased by 61±13% (P<0.005) but more surprisingly the amplitude of the [Ca2+]i transient increased by 156±10%, compared to control (P<0.001) i.e. to an extent almost similar to that seen during prolonged exposures.
Conclusion: Data imply that the increased CICR on a beat-beat basis may be a consequence of a extremely rapid phosphorylation of the RYR due to synergistic effect between high [Ca2+]o and ß1-adrenergic stimulation, therefore increasing SR Ca2+ fractional release.
- Excitation-contraction coupling (ECC)
- Ion channels
- Beta-adrenergic receptor agonists
- © 2013 by American Heart Association, Inc.