LINEARIZED BUFFERED CA2-CHANNEL( DIFFUSION IN MICRODOMAINS AND ITS IMPLICATIONS FOR CALCULATION OF [CA2+] AT THE MONTH OF A CALCIUM)

Immobile and mobile calcium buffers shape the calcium signal close to a channel by reducing and localizing the transient calcium increase to physiological compartments, in this paper, we focus on the impact of mobile buffers in shaping steady-state calcium gradients in the vicini ty of an open channel, i.e. within its ''calcium microdomain.'' We pre sent a linear approximation of the combined reaction-diffusion problem , which can be solved explicitly and accounts for an arbitrary number of calcium buffers, either endogenous or added exogenously, It is vali d for small saturation levels of the present buffers and shows that wi thin a few hundred nanometers from the channel, standing calcium gradi ents develop in hundreds of microseconds after channel opening. It is shown that every buffer can be assigned a uniquely defined length-cons tant as a measure of its capability to buffer calcium close to the cha nnel, The length-constant clarifies intuitively the significance of bu ffer binding and unbinding kinetics for understanding local calcium si gnals. Hence, we examine the parameters shaping these steady-state gra dients, The model can be used to check the expected influence of singl e channel calcium microdomains on physiological processes such as exci tation-secretion coupling or excitation-contraction coupling and to ex plore the differential effect of kinetic buffer parameters on the shap e of these microdomains.