Thalamic neurons display robust low voltage-activated (LVA or T-type) calcium current that plays pivotal role in the generation of low threshold calcium spikes (LTCS) and bursting activity. Though a plenty of information about the functional properties of T-type channels there is few evidence about their regulation. In acutely isolated neurons, expressed mRNAs for a1G, a1H and a1I T-channel a1-subunits in approximate ratio 1,0:0,46:0,85, as assayed by single-cell RT-PCR (n=15), equimolar substitution of extracellular Cs⁺ for Na⁺ in the presence of 2,5 mM Ca²⁺ as a major charge carrier led to the notable increase in the net LVA current amplitude, while replacement of TEA⁺ for Na⁺ had almost no effect(I_Na:I_Cs:I_TEA=1:1,21:1,03). Surprisingly, in the cultured neurons, which had similar expression of T-channel a1-subunits mRNA to the acutely isolated ones (n=8), we were unable to detect any LVA current in solutions containing Ca²⁺ in combination with Na⁺ or TEA⁺. However, in presence of Cs⁺ LVA current with characteristic properties was readily detectable. Our results suggest that Cs⁺ may modulate and/or permeate through T-type Ca²⁺-channels and that permeation properties of the channels may be regulated by some additional factor(s) and/or subunits, which are differentially expressed in acutely vs. cultured thalamic neurons. Alternatively, the possibility of a novel Cs⁺activated T-type channel in thalamic neurons may exist.