Voltage-activated intracellular calcium transients in thalamic relay cells and interneurons

The dynamics of intracellular calcium concentration ([Ca2+](i)) following activation of low voltage-activated (LVA) and high voltage-activated (HVA) Ca2+ currents were studied in identified relay neurons and interneurons of the rat dorsal lateral geniculate nucleus (LGNd) in situ using Ca2+ imaging and patch-clamp techniques. In relay neurons, [Ca2+](i) transients associated with the LVA Ca2+ current showed a fairly homogeneous somatodendritic distribution, whereas HVA transients significantly decreased to 65% of the somatic value at 60 mu m dendritic distance. In interneurons, LVA transients significantly increased to 239% of the somatic value at 60 mu m dendritic distance, whereas HVA transients were not significantly different in the soma and dendrites. These results indicate differences in [Ca2+](i) dynamics, which may reflect a heterogeneous distribution of Ca2+ channels contributing to subcellular compartmentation in the two types of thalamic neurons.