Cutaneous
ATP release plays an important role in both epidermal stratification and
chronic pain, but little is known about
ATP release mechanisms in keratinocytes that comprise the epidermis. In this study, we analyzed
ATP release from cultured human neonatal keratinocytes briefly exposed to air, a process previously demonstrated to trigger
ATP release from these cells. We show that exposing keratinocytes to air by removing media for 15 seconds causes a robust, long-lasting
ATP release. This air-stimulated
ATP release was increased in
calcium differentiated cultures which showed a corresponding increase in
connexin 43 mRNA, a major component of keratinocyte hemichannels. The known
connexin hemichannel inhibitors
1-octanol and
carbenoxolone both significantly reduced air-stimulated
ATP release, as did two drugs traditionally used as
ABC transporter inhibitors (
glibenclamide and
verapamil). These same 4 inhibitors also prevented an increase in the uptake of a
connexin permeable
dye induced by air exposure, confirming that
connexin hemichannels are open during air-stimulated
ATP release. In contrast, activity of the MDR1
ABC transporter was reduced by air exposure and the drugs that inhibited air-stimulated
ATP release had differential effects on this transporter. These results indicate that air exposure elicits non-vesicular release of
ATP from keratinocytes through
connexin hemichannels and that drugs used to target
connexin hemichannels and
ABC transporters may cross-inhibit.
Connexins represent a novel, peripheral target for the treatment of
chronic pain and dermatological disease.