Our previous work demonstrated that in sensory neurons maint

Our previous work demonstrated that in sensory Amiloride HCl maintained in the presence of NGF, PGE2 enhances evoked AP firing and neurotransmitter release in an Epac-dependent mechanism. In the current study, we demonstrate that direct activation of Epacs in sensory neurons activates both Ras and Rap1 small GTPase proteins; however, in capsaicin-sensitive sensory neurons, the ability of the Epac agonist to enhance AP firing and neurotransmitter release is blocked by inhibition Ras and not Rap1 (Fig. 9). Our demonstration that sensitization of capsaicin-sensitive sensory neurons grown in NGF occurs through activation of the Epac-Ras signaling cascade provides a novel signaling pathway that could serve as an ideal therapeutic target in the treatment of chronic pathological pain without altering the ability to respond to normal physiological sensations.
Conflict of interest > Acknowledgments M.R.V. conceived the overall design of the project. B.S., G.D.N., and M.R.V. conceived and designed the experiments. B.S. performed the experiments and analyzed the data. B.S., G.D.N., and M.R.V. interpreted results of experiments. E.L.T. generously provided the dominant-negative Ras lentiviral particles and offered critical feedback. B.S. and M.R.V prepared figures. B.S. drafted the manuscript. G.D.N. and M.R.V. edited and revised the manuscript. We would like to thank Dr. Jill C. Fehrenbacher for valuable suggestions regarding experimental design with dominant negative Ras and Drs. Ruizong Wang and Yihong Zhang for technical assistance. This work was supported by NIH Grant NS069915 to MRV. These studies were conducted, in part, in a facility constructed with the support from the Research Facilities Improvement Program Grant Number C06 RR015481-01 from the National Center for Research Resources, National Institutes of Health.
Introduction Whereas the physiological and pathological effects of the universal second messenger 3′,5′-cyclic adenosine monophosphate (cAMP) were believed to be mediated exclusively by protein kinase A (PKA) and cyclic nucleotide-regulated ion channels, it has been also shown that the existence of a PKA-independent mechanism of cAMP action is mediated by a family of guanine nucleotide exchange factors, the Exchange Protein directly Activated by Cyclic AMP (EPAC) [1]. EPAC isoforms have important roles in several human diseases notably in heart failure [2], [3], [4]. Sustained EPAC activation is involved in cardiac hypertrophy [5] by initiating the Ca2+ dependent excitation-transcription coupling [6], [7], [8]. Several pathways can serve to increase [Ca2+]i in the cardiac myocyte, e.g. the L-type Ca2+ channels (LTCC), the Na+/Ca2 exchanger (NCX), the ryanodine receptor (RyR) and the SERCA pump [9]. However, it has been shown that, when over-expressed, Transient Receptor Potential Canonical (TRPC) channels can initiate cardiac hypertrophy through increased Ca2+ influx and calcineurin/NFAT activation [2], [10].