Effects of rapid buffers on Ca2+ diffusion and Ca2+ oscillations.
Based on realistic mechanisms of Ca2+ buffering that include both stationary and mobile buffers, we derive and investigate models of Ca2+ diffusion in the presence of rapid buffers. We obtain a single transport equation for Ca2+ that contains the effects caused by both stationary and mobile buffers. For stationary buffers alone, we obtain an expression for the effective diffusion constant of Ca2+ that depends on local Ca2+ concentrations. Mobile buffers, such as fura-2, BAPTA, or small endogenous proteins, give rise to a transport equation that is no longer strictly diffusive. Calculations are presented to show that these effects can modify greatly the manner and rate at which Ca2+ diffuses in cells, and we compare these results with recent measurements by Allbritton et al. (1992). As a prelude to work on Ca2+ waves, we use a simplified version of our model of the activation and inhibition of the IP3 receptor Ca2+ channel in the ER membrane to illustrate the way in which Ca2+ buffering can affect both the amplitude and existence of Ca2+ oscillations.
Wagner
J
J
Institute of Theoretical Dynamics, University of California, Davis 95616.
Keizer
J
J
D000818:Animals; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D009991:Oscillometry; D013997:Time Factors
D002021:Buffers; D002413:Cations, Divalent; D005456:Fluorescent Dyes; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; D016257:Fura-2