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 neurotransmitter release. In the present work we calculate the magnitude and the time course of Ca²⁺ domains that evolve in the vicinity of a Ca²⁺ channel and an adjacent release site. In the calculations we consider a accurately dimensioned Ca²⁺ channel. Moreover, the Ca²⁺ current is continuously adjusted with regard to the accumulated intracellular Ca²⁺ and, in addition, endogenous buffers are considered. The calculations, carried out by the software FIDAP, based on finite element method, show that the Ca²⁺ concentrations achieved near the release sites are 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.