Cyclic AMP regulates the calcium transients released from IP3-sensitive stores by activation of rat kappa-opioid receptors expressed in CHO cells

We analyzed intracellular Ca2+ and cAMP levels in Chinese hamster ovary cel ls expressing a cloned rat kappa opioid receptor (CHO-kappa cells). Althoug h expression of kappa (kappa)-opioid receptors was confirmed with a fluores cent dynorphin analog in almost all CHO-kappa cells, the kappa -specific ag onists, U50488H or U69593, induced a Ca2+ transient only in 35% of the cell s. The Ca2+ response occurred in all-or-none fashion and the half-maximal d osage of U50488H (812.1 nM) was higher than that (3.2 nM) to inhibit forsko lin-stimulated cAMP. The kappa -receptors coupled to G(i/o) proteins since pertussis toxin significantly reduced the U50488H actions on intracellular Ca2+ and cAMP. The Ca2+ transient originates from IP3-sensitive internal st ores since the Ca2+ response was blocked by a PLC inhibitor (U73122) or by thapsigargin depletion of internal stores while removal of extracellular Ca 2+ had no effect. interestingly application of dibutyryl cAMP (+56.2%) or 8 -bromo-cAMP (+174.7%) significantly increased the occurrence of U50488H-ind uced Ca2+ mobilization while protein kinase A (PKA) inhibitors, Rp-cAMP (-3 2.3%) or myr-psi PKA (-73.9%) significantly reduced the response. Therefore , it was concluded that cAMP and PKA activity can regulate the Ca2+ mobiliz ation. These results suggest that the kappa receptor-linked cAMP cascade re gulates the occurrence of kappa -opioid-mediated Ca2+ mobilization. (C) 200 1 Harcourt Publishers Ltd.