Figure 6

(A) Naloxone reverses morphine-inhibition of FSK-potentiated TRPV1 Ca²⁺ responses. Fluo-3 loaded FLAG-MOP/TRPV1 double expressants (Colony 21) were pre-incubated with PSS for untreated cells (*) or morphine (1 μM) and naloxone (50 μM) as appropriate for treated cells for 15 min, followed by incubation with PSS for unstimulated cells or FSK (50 μM) and IBMX (100 μM) for stimulated cells. Pre-treatment with the opioid receptor antagonist naloxone (50 μM) (◊) prevented inhibition of FSK-potentiated capsaicin (300 nM) responses (●) by morphine (x). (B) Pre-incubation with morphine and activation of second messenger systems is required for morphine-inhibition of FSK-potentiated capsaicin responses. Fluo-3 loaded FLAG-MOP/TRPV1 double expressants (Colony 21) were pre-incubated with PSS for unstimulated cells (*) or FSK (50 μM) and IBMX (100 μM) for stimulated cells. Injection of morphine (◊) to a well concentration of 1 μM alongside capsaicin (300 nM) did not affect capsaicin (300 nM) responses in FSK-stimulated cells (●). Data are presented as mean ± SEM for n = 8 and statistical significance was determined at peak Ca²⁺ responses after addition of capsaicin. * p < 0.05 for FSK+morphine compared to FSK alone.