Activation and Desensitization of TRPV1 Channels under the Influence of Capsaicin

The work was carried out on primary cultures of neurons (1- to 2-day-long cultivation) isolated from DRGs of 8- to 12-day-old rats; fluorescent microscopy was used for evaluation of the level of intracellular calcium in the studied units. Small-sized neurons supposedly attributable to nociceptors (diameter 21–37 μm and mean surface area 589 ± 96 μm2) were selected. Capsaicin (100 nM) was applied for 5–10 sec with 2- to 3-min-long intervals. After 30–40 min, this protocol was continued by application of 100 μM uridine-5’-triphosphate for 1–2 min; then capsaicin was applied again. All DRG neurons demonstrating calcium responses to capsaicin could be divided into four groups, units with slow-enhancing capsaicin effects demonstrating desensitization (n = 30; 49%), those with rapidly developing capsaicin effects followed by desensitization (n = 12; 20%), neurons with rapid capsaicin responses and no desensitization (n = 11; 18%), and units with slow responses with no desensitization (n = 8; 13%). Applications of uridine-5’-triphosphate (UTP) to capsaicin-affected neurons with desensitization caused full or partial resensitization of TRPV1 receptors.