Participation of intracellular Ca2+ stores in Ca2+ signalling in neurons of the thalamic laterodorsal nucleus of rats

Experiments were carried out on isolated neurons of the thalamic nucleus lateralis dorsalis (LD) from 12-day-old rats. According to the morphological characteristics. LD neurons were classified as relay thalamo-cortical units and interneurons. The concentration of free Ca2- ions in the cytoplasm ([Ca2-],) was measured by a fluorescent calcium indicator, fura-2AM. Application of 30 mM caffeine caused a transient change in the [Ca2-], in 8 of 15 and in 6 of 11 of the thalamo-cortical units and interneurons under study. respectively. After stimulation of a cell with application of 50 mM KCl, a caffeine-induced increase in the [Ca2+], was observed in all tested neurons. To study the contribution of Ca2--induced Ca2- release (CICR) to the calcium transient evoked by depolarization of the neuronal membrane, caffeine in a subthreshold concentration was prc-applied. After 50 mM KCl had been added to the medium following pre-application of 0.5 mM caffeine, the calcium transient amplitude in thalamo-cortical neurons increased by 51 +/- 7% (n = 16). In interneurons this effect was not observed (n = 11). The data obtained allow us to hypothesize that CICR contributes to the depolarization-evoked calcium transient only in the relay (thalamo-cortical) neurons. Differences in the pattern of calcium signalling. which were detected in two types of neurons of the thalamic LD, can be a factor determining distinctions in the physiological characteristics of these neurons.