Ca2+ transient evoked by chemical stimulation is enhanced by PGE2 in vagal sensory neurons:: Role of cAMP/PKA signaling pathway

The effect of prostaglandin E-2 (PGE(2)) 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 x 10(-8) to 10(-7) M; 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 PGE(2) (3 x 10(-7) M; 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 PGE(2) gradually declined but remained higher than control after 15-min washout. Similarly, PGE(2) pretreatment 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 PGE(2) to 242, 204, and 163% of their control, respectively. This potentiating effect of PGE(2) could be mimicked by forskolin (10(-6) M; 5 min), an activator of adenylyl cyclase, and 8-(4-chlorophenylthio)adenosine-3'-5'-cyclic monophosphate (CPT-cAMP; 3 x 10(-6) M, 10 min), a membrane-permeable cAMP analogue. Furthermore, the potentiating effects of PGE(2), forskolin, and CPT-cAMP were abolished by N-[2-(p-bromocinnamylamino) ethyl]-5-isoquinolinesulfonamide (H89; 10(-5) M; 15-20 min), a protein kinase A (PKA) inhibitor. In summary, these results show that PGE(2) reversibly 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.