Role of inositol 1,4,5-trisphosphate in the regulation of ventricular Ca(2+) signaling in intact mouse heart

• Published in: Journal of molecular and cellular cardiology 2012-12, Vol.53 (6), p.768
• Main Authors: Escobar, Ariel L, Perez, Claudia G, Reyes, Mariano E, Lucero, Sarah G, Kornyeyev, Dmytro, Mejía-Alvarez, Rafael, Ramos-Franco, Josefina
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Animals; Calcium - metabolism; Calcium Signaling - drug effects; Dose-Response Relationship, Drug; Heart - drug effects; Heart - physiology; Heart Ventricles - drug effects; Heart Ventricles - metabolism; In Vitro Techniques; Inositol 1,4,5-Trisphosphate - metabolism; Inositol 1,4,5-Trisphosphate - pharmacology; Inositol 1,4,5-Trisphosphate Receptors - metabolism; Kinetics; Mice; Myocytes, Cardiac - metabolism; Protein Binding; Ryanodine Receptor Calcium Release Channel - metabolism
• ISSN: 1095-8584
• DOI: 10.1016/j.yjmcc.2012.08.019

Inositol 1,4,5-trisphosphate (InsP(3)R)-mediated Ca(2+) signaling is a major pathway regulating multiple cellular functions in excitable and non-excitable cells. Although InsP(3)-mediated Ca(2+) signaling has been extensively described, its influence on ventricular myocardium activity has not been addressed in contracting hearts at the whole-organ level. In this work, InsP(3)-sensitive intracellular Ca(2+) signals were studied in intact hearts using laser scanning confocal microscopy and pulsed local-field fluorescence microscopy. Intracellular [InsP(3)] was rapidly increased by UV flash photolysis of membrane-permeant caged InsP(3). Our results indicate that the basal [Ca(2+)] increased after the flash photolysis of caged InsP(3) without affecting the action potential (AP)-induced Ca(2+) transients. The amplitude of the basal [Ca(2+)] elevation depended on the intracellular [InsP(3)] reached after the UV flash. Pretreatment with ryanodine failed to abolish the InsP(3)-induced Ca(2+) release (IICR), indicating that this response was not mediated by ryanodine receptors (RyR). Thapsigargin prevented Ca(2+) release from both RyR- and InsP(3)R-containing Ca(2+) stores, suggesting that these pools have similar Ca(2+) reuptake mechanisms. These results were reproduced in acutely isolated cells where photorelease of InsP(3) was able to induce changes in endothelial cells but not in AP-induced transients from cardiomyocytes. Taken together, these results suggest that IICR does not directly regulate cardiac excitation-contraction coupling. To our knowledge, this is the first demonstration of IICR in intact hearts. Consequently, our work provides a reference framework of the spatiotemporal attributes of the IICR under physiological conditions.