How Ca2+-Activated, cAMP/PKA-Dependent Phosphorylation Signaling Mediates Pacemaker Cell Activity: Experimental and In Silico Biochemical and Biophysics Perspectives

Abstract

Ca2+-activated, adenylate cyclase (AC)-cAMP/PKA-dependent phosphorylation of both surface membrane electrogenic proteins of (“Membrane-clock”), and of intracellular proteins that generate rhythmic Ca2+ oscillations (“Ca2+-clock”), regulate the periodicity of each clock, and couple the two-clocks to regulate sinoatrial node cells (SANCs) normal automaticity.We developed a novel numerical model to simulate the coupling of SANC Ca2+-AC-cAMP/PKA signaling to functions of surface membrane and Ca2+ cycling molecules. The model incorporates experimentally measured a term for Ca2+-dependent AC-activity, and when Ca2+ changes predicts resulting changes in downstream cAMP/PKA phosphorylation-dependent signaling that produce changes in ion channels conductance and intracellular Ca2+ kinetics that ultimately change the spontaneous action potential (AP) firing rate.Model predictions of Ca2+-dependent changes in the cAMP/PKA phosphorylation cascade, of spontaneous AP firing rate and of the stoichiometry-relationships between cAMP, phospholamban phosphorylation and AP firing rate (line in the figure) faithfully reproduced the experimentally measured variables and their stoichiometry (points in the figure).The simulations of this novel integrative model of biochemical and biophysical signaling within the coupled-clock model further support the importance of high throughput signaling via Ca2+-AC-cAMP-PKA phosphorylation cascade in normal SANC automaticity.View Large Image | View Hi-Res Image | Download PowerPoint Slide