Ca2+ spark dynamics in cardiac myocyte

摘要

Ca2+, one of the most classical messengers in living cells, regulates many important life processes, from hormone secretion to muscle contraction, nerve signal transduction to learning and memory, gene expression to protein phosphorylation. But how can Ca2+ take on such a wide range of physiological functions? The relations among these functions, sorts of Ca2+ channels, space distribution, kinetic control, and Ca2+ buffering and diffusion in cell microenvironment, are essential problems for research on Ca2+ signal transduction and important foundation for elucidating cell function, growth, signal process and pathology. Cheng et al. first demonstrated that Ca2+ release from the sarcoplasmic reticulum (SR) occurs as discrete quanta[1]. They named these quanta Ca2+ sparks because of the brief localized light emission they induced in Ca2+sensitive fluorescent dyes. Since their discovery, Ca2+ sparks have been found in cardiac, skeletal, and smooth muscle cells and provide molecular interpretations for intercellular Ca2+ signal transduction[2-4]. However, in the opinion of biomechanics, Ca2+ spark is a dynamic process of random point source diffusion and chemical reactions of substances in the cell. The classical Fickian diffusion e-quation and reaction-kinetic model have been widely used to describe the process. However, recent work suggests that even the minimum spatial scale of Ca2+ spark is still much larger than that simulated by the Fickian diffusion model [5]. Based on the diffusion phenomenon of Ca2+ spark in cardiac myocytes, an essential question on unit calcium signal has been put forward: whether the diffusion of calcium spark obeys Fickian diffusion, if not, why? Furthermore, which rule and theory can best describe kinetics of this anomalous diffusion. These are very important to elucidate how Ca2+ molecular channel produces gradient of calcium signal, how different gradients activate different target sites and downstream signal pathway, and consequently control different life process in the cell.