THE MAGNITUDE AND SIGNIFICANCE OF CA2+ DOMAINS FOR RELEASE OF NEUROTRANSMITTER

It is now widely accepted that localized high concentrations of Ca2+ ( Ca2+ domains) play a major role in controlling the time course of neur otransmitter release. In the present work we calculate the magnitude a nd the time course of Ca2+ domains that evolve in the vicinity of a Ca 2+ channel and an adjacent release site. In the calculations we consid er a accurately dimensioned Ca2+ channel. Moreover, the Ca2+ current i s continuously adjusted with regard to the accumulated intracellular C a2+ and, in addition, endogenous buffers are considered. The calculati ons, carried out by the software FIDAP, based on finite element method , show that the Ca2+ concentrations achieved near the release sites ar e significantly lower than claimed by other investigators. Furthermore , we present arguments indicating that the Ca2+ domains, regardless of their magnitude, do not play a role in controlling the time course of release of neurotransmitter.