Submitted on September 17, 2007
Accepted on April 16, 2008
Up-regulation of the T-type calcium current in small rat sensory neurons after chronic constrictive injury of the sciatic nerve
Miljen M Jagodic1, Sriyani Pathirathna1, Pavle M Joksovic1, WooYong Lee1, Michael T Nelson1, Ajit K Naik1, Peihan Su1, Vesna Jevtovic-Todorovic1, and Slobodan M Todorovic1*
1 Anesthesiology, UVA, Charlottesville, Virginia, United States
* To whom correspondence should be addressed. E-mail: st9d{at}virginia.edu.
Recent data indicate that peripheral T-type Ca2+ channels are instrumental in supporting acute pain transmission. However, the function of these channels in chronic pain processing is less clear. To address this issue, we studied the expression of T-type Ca2+ currents in small nociceptive dorsal root ganglion (DRG) cells from L4-5 spinal ganglia of adult rats with neuropathic pain due to chronic constrictive injury (CCI) of the sciatic nerve. In control rats, whole-cell recordings revealed that T-type currents, measured in 10 mM Ba2+ as a charge carrier, were present in moderate density (20± 2 pA/pF). In rats with CCI, T-type current density (30± 3 pA/pF) was significantly increased, but voltage- and time-dependent activation and inactivation kinetics were not significantly different from those in controls. CCI-induced neuropathy did not significantly change the pharmacological sensitivity of T-type current in these cells to nickel. Collectively, our results indicate that CCI-induced neuropathy significantly increases T-type current expression in small DRG neurons. Our finding that T-type currents are up-regulated in a CCI model of peripheral neuropathy and earlier pharmacological and molecular studies suggest that T-type channels may be potentially useful therapeutic targets for the treatment of neuropathic pain associated with partial mechanical injury to the sciatic nerve.
