Nociceptive Neurons Differentially Express Fast and Slow T-Type Ca²⁺ Currents in Different Types of Diabetic Neuropathy

Figure 2

Fast and slow T-currents expressed by NTCN neurons reveal different sensitivity to low Ni²⁺ concentration. (a) Representative current traces illustrate effect of Ni²⁺ application to NTCN neurons of naive rats expressing fast (left) and slow (right) T-currents. Initial (total) T-current traces are shown in black while grey traces represent a residual Ni²⁺-insensitive component of T-current persisted during Ni²⁺ application. Note the considerably larger blocking effect of Ni²⁺ application on the fast compared to slow T-currents. Insets show the total and Ni²⁺-insensitive currents normalized by their amplitudes in order to directly compare their inactivation kinetics further shown in (c). Note the slower inactivation of Ni²⁺-insensitive component compared to the total current for the case of slow T-current. Scale bars shown in (a) are applicable to all current traces in (a) and (b). (b) Representative traces for a Ni²⁺-sensitive component of fast (left) and slow (right) T-currents were obtained by digital subtraction of the Ni²⁺-insensitive component from the total T-current for traces shown in (a). Insets demonstrate normalized Ni²⁺-sensitive (gray) and Ni²⁺-insensitive (black) components. Note the absence of visible difference in kinetics of inactivation between these components of the fast T-current and a substantially slower Ni²⁺-insensitive component as compared to the Ni²⁺-sensitive one for the case of slow T-current. (c) Fractions of Ni²⁺-insensitive component in the fast and slow T-currents were significantly different. *-𝑃<0.05. (d) A ratio of inactivation kinetics of Ni²⁺-insensitive component and the total T-current for NTCN neurons expressing the fast and slow T-currents. There were no significant changes observed in the case of fast T-current (𝑃>0.4), while the inactivation kinetics of Ni²⁺-insensitive component of slow T-current was significantly slower compared to the inactivation kinetics of the total current. **-𝑃<0.01. (e) Inactivation kinetics of Ni²⁺-sensitive components of fast and slow T-currents. n.s.: no significant difference was revealed between the inactivation kinetics of Ni²⁺-sensitive components of the fast and slow T-currents (𝑃>0.3). Each column in (c), (d), and (e) is the mean and SEM from 6 fast and 3 slow T-currents.

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