Functional Expression of T-Type Ca2+ Channels in Spinal Motoneurons of the Adult Turtle

Voltage-gated Ca2+ (Ca-V) channels are transmembrane proteins comprising three subfamilies named Ca(V)1, Ca(V)2 and Ca(V)3. The Ca(V)3 channel subfamily groups the low-voltage activated Ca2+ channels (LVA or T-type) a significant role in regulating neuronal excitability. Ca(V)3 channel activity may lead to the generation of complex patterns of action potential firing such as the postinhibitory rebound (PIR). In the adult spinal cord, these channels have been found in dorsal horn interneurons where they control physiological events near the resting potential and participate in determining excitability. In motoneurons, Ca(V)3 channels have been found during development, but their functional expression has not yet been reported in adult animals. Here, we show evidence for the presence of Ca(V)3 channel-mediated PIR in motoneurons of the adult turtle spinal cord. Our results indicate that Ni2+ and NNC55-0396, two antagonists of Ca(V)3 channel activity, inhibited PIR in the adult turtle spinal cord. Molecular biology and biochemical assays revealed the expression of the Ca(V)3.1 channel isotype and its localization in motoneurons. Together, these results provide evidence for the expression of Ca(V)3.1 channels in the spinal cord of adult animals and show also that these channels may contribute to determine the excitability of motoneurons.