Abstract 820: Autoregulation of CGRP Expression via β 2 -Adrenoreceptor Signaling in Intrinsic Cardiac Adrenergic Cells

Abstract

Background : Calcitonin gene-related peptide (CGRP) is a neuropeptide with broad salutary cardiovascular effects. Mechanisms underlying cardiac CGRP regulation are poorly understood. The intrinsic cardiac adrenergic (ICA) cell is a novel cardiac neuroendocrine cell that expresses the δ-opioid receptor. We have shown that δ-opioid stimulation of ICA cells induces epinephrine liberation exerting an infarct-size limiting effect via β 2 -adrenoreceptor (β 2 -AR) stimulation. In this study we hypothesize that ICA cells synthesize and release CGRP which is involved in myocardial function and that CGRP gene expression can be autoregulated by epinephrine released from the ICA cell or regulated exogenously via β 2 -AR agonist. Methods and Results : In situ hybridization coupled with immunofluorescent double labeling localized CGRP mRNA expression exclusively to ICA cells in explanted human left ventricular tissue. To determine whether δ-opioid-enhanced epinephrine release from ICA cells autoregulates CGRP gene expression, isolated and cultured (for 2-weeks) adult rat ICA cells were treated with δ-opioid agonist DPDPE (0.1 μM for 1h) in the absence and presence of the β 2 -AR antagonist ICI-118551 (ICI, 10 μM). DPDPE induced 4-fold increase in CGRP mRNA at 6h post DPDPE-treatment by real-time PCR. This effect was abolished in the presence of ICI. To confirm the epinephrine-β 2 -AR signaling pathway, exogenous epinephrine was applied (0.1 μM for 1h) to ICA cells in the absence and presence of ICI (10 μM). Epinephrine induced 16-fold increase in CGRP mRNA levels at 6h post-treatment. This effect was completely abolished in the presence of ICI. To determine whether endogenous CGRP release from ICA cells exerts tonic modulation on myocyte contractile function, we studied the interaction between ICA cells and myocytes in ICA cell-myocyte co-culture model using a ratio fluorescent spectrometer. Application of CGRP-receptor antagonist CGRP 8 –37 (0.2 μM) reduced myocyte [Ca 2+ ]i transients by 30 ± 5%. Conclusion s: ICA cells exclusively express CGRP gene in human and animal hearts. Robust and sustained CGRP gene-expression can be induced via β 2 -AR signaling through autocrine epinephrine positive feedback or pharmacological β 2 -AR stimulation.