Ca2+Transient Evoked by Chemical Stimulation Is Enhanced by PGE2in Vagal Sensory Neurons: Role of cAMP/PKA Signaling Pathway

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Abstract
The effect of prostaglandin E2(PGE2) on chemical stimulation-evoked calcium (Ca2+) transient was investigated in isolated vagal sensory neurons of the rat using fura-2-based ratiometric Ca2+imaging. Application of capsaicin (3 × 10−8to 10−7M; 15 s) caused a rapid surge of intracellular Ca2+concentration in small- and medium-size neurons; the response was reproducible when >10 min elapsed between two challenges and was absent in nominally Ca2+-free solution. After pretreatment with PGE2(3 × 10−7M; 5 min), the peak of this capsaicin-evoked Ca2+transient was increased by almost fourfold, and its duration was also prolonged. This augmented response to capsaicin induced by PGE2gradually declined but remained higher than control after 15-min washout. Similarly, PGE2pretreatment also markedly enhanced the Ca2+transients induced by other chemical stimulants to C neurons, such as phenylbiguanide (PBG), adenosine 5′-triphosphate (ATP), and KCl. The Ca2+transients evoked by PBG, ATP, and KCl were potentiated after the pretreatment with PGE2to 242, 204, and 163% of their control, respectively. This potentiating effect of PGE2could be mimicked by forskolin (10−6M; 5 min), an activator of adenylyl cyclase, and 8-(4-chlorophenylthio)adenosine-3′-5′-cyclic monophosphate (CPT-cAMP; 3 × 10−6M, 10 min), a membrane-permeable cAMP analogue. Furthermore, the potentiating effects of PGE2, forskolin, and CPT-cAMP were abolished by N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H89; 10−5M; 15–20 min), a protein kinase A (PKA) inhibitor. In summary, these results show that PGE2reversibly potentiates the chemical stimuli-evoked Ca2+transients in cultured rat vagal sensory neurons, and this potentiating effect is mediated through the cyclic AMP/PKA transduction cascade.