Blockade of N- and P/Q-type calcium channels reduces the secondary heat hyperalgesia induced by acute inflammation.

High voltage calcium channels are implicated in nociceptive transmission after nerve injury, capsaicin or formalin injection. The purpose of this study was to investigate the role of calcium channels in secondary heat hyperalgesia associated with acute joint inflammation. After induction of acute inflammation (knee joint injection of kaolin and carrageenan), decreased paw withdrawal latency (PWL) to radiant heat (i.e., secondary heat hyperalgesia), increased guarding of the limb and increased joint circumference occurs. Spinal administration (through a microdialysis fiber placed in dorsal horn) of an N-type calcium channel blocker (MVIIA, SNX 111, ziconotide, 0.001-0.1 mM), before induction of inflammation, prevents the decrease in PWL. Treatment with SNX 111 4 hr after inflammation reverses heat hyperalgesia. A small reduction in spontaneous pain-related behaviors (guarding of the limb) occurs after pre- or post-treatment with SNX 111. Spinal blockade of P/Q-type calcium channels (with omega-agatoxin IVA) had no effect on the decrease in PWL to radiant heat when administered after induction of inflammation. However, pre-treatment with omega-agatoxin IVA prevents secondary heat hyperalgesia. omega-Agatoxin IVA has no effect on spontaneous pain-related behaviors whether administered before or after induction of inflammation. In contrast, pre or post-treatment with nifedipine (L-type calcium channel blocker, 0.01-1.0 mM), had no effect on heat hyperalgesia or spontaneous pain-related behaviors induced by acute inflammation. There were no differences in joint circumference between groups with any treatment. Thus, N-type calcium channels contribute to both the development and maintenance of secondary heat hyperalgesia while P-type calcium channels are only involved during development of hyperalgesia.