Activation of IP 3 R in atrial cardiomyocytes leads to generation of cytosolic cAMP

• Published in: American journal of physiology. Heart and circulatory physiology Vol. 327; no. 4; p. H830
• Main Authors: Akerman, Emily C, Read, Matthew J, Bose, Samuel J, Koschinski, Andreas, Capel, Rebecca A, Chao, Ying-Chi, Folkmanaite, Milda, Ayagama, Thamali, Broadbent, Steven D, Ahamed, Rufaida, Simon, Jillian N, Terrar, Derek A, Zaccolo, Manuela, Burton, Rebecca A B
• Format: Journal Article
• Language: English
• Published: United States 01-10-2024
• Subjects: Animals; Animals, Newborn; Boron Compounds - pharmacology; Calcium Signaling - drug effects; Cells, Cultured; Cyclic AMP - metabolism; Cytosol - metabolism; Fluorescence Resonance Energy Transfer; Heart Atria - cytology; Heart Atria - drug effects; Heart Atria - metabolism; Inositol 1,4,5-Trisphosphate - metabolism; Inositol 1,4,5-Trisphosphate Receptors - metabolism; Myocytes, Cardiac - drug effects; Myocytes, Cardiac - metabolism; Phenylephrine - pharmacology; Rats; Rats, Sprague-Dawley; Second Messenger Systems - drug effects; Ca2+ signaling; cardiac atria; adenylyl cyclase; cyclic AMP; inositol trisphosphate
• ISSN: 1522-1539

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia. Excessive stimulation of the inositol (1,4,5)-trisphosphate (IP
) signaling pathway has been linked to AF through abnormal calcium handling. However, little is known about the mechanisms involved in this process. We expressed the fluorescence resonance energy transfer (FRET)-based cytosolic cyclic adenosine monophosphate (cAMP) sensor EPAC-S
in neonatal rat atrial myocytes (NRAMs) and neonatal rat ventricular myocytes (NRVMs). In NRAMs, the addition of the α
-agonist, phenylephrine (PE, 3 µM), resulted in a FRET change of 21.20 ± 7.43%, and the addition of membrane-permeant IP
derivative 2,3,6-tri-
-
-myo-IP
(1,4,5)-hexakis(acetoxymethyl)ester (IP
-AM, 20 μM) resulted in a peak of 20.31 ± 6.74%. These FRET changes imply an increase in cAMP. Prior application of IP
receptor (IP
R) inhibitors 2-aminoethyl diphenylborinate (2-APB, 2.5 μM) or Xestospongin-C (0.3 μM) significantly inhibited the change in FRET in NRAMs in response to PE. Xestospongin-C (0.3 μM) significantly inhibited the change in FRET in NRAMs in response to IP
-AM. The FRET change in response to PE in NRVMs was not inhibited by 2-APB or Xestospongin-C. Finally, the localization of cAMP signals was tested by expressing the FRET-based cAMP sensor, AKAP79-CUTie, which targets the intracellular surface of the plasmalemma. We found in NRAMs that PE led to FRET change corresponding to an increase in cAMP that was inhibited by 2-APB and Xestospongin-C. These data support further investigation of the proarrhythmic nature and components of IP
-induced cAMP signaling to identify potential pharmacological targets.
This study shows that indirect activation of the IP
pathway in atrial myocytes using phenylephrine and direct activation using IP
-AM leads to an increase in cAMP and is in part localized to the cell membrane. These changes can be pharmacologically inhibited using IP
R inhibitors. However, the cAMP rise in ventricular myocytes is independent of IP
R calcium release. Our data support further investigation into the proarrhythmic nature of IP
-induced cAMP signaling.