5-Hydroxytryptamine2B receptor signaling in rat stomach fundus: role of voltage-dependent calcium channels, intracellular calcium release and protein kinase C.

The rat stomach fundus is enriched with the 5-hydroxytryptamine (5-HT)2B receptor, the newest subtype of the 5-HT2 receptor family to be cloned. Although the 5-HT2A and 5-HT2C receptor subtypes couple to phosphatidylinositol hydrolysis, such a coupling has not been established for the 5-HT2B receptor in tissues. Thus, the purpose of this study was to characterize further the signal transduction mechanism of the 5-HT2B receptor in rat stomach fundus. Nitrendipine (1 microM) inhibited the maximal contraction to 5-HT (1 microM) by approximately 50%. Removal of extracellular calcium did not inhibit 5-HT contraction to a greater extent than that produced by nitrendipine, indicating that calcium influx through voltage-dependent calcium channels was predominantly responsible for the dependence of the 5-HT contraction on extracellular calcium. Depletion of both extracellular calcium and intracellular calcium stores abolished 5-HT contraction. Ryanodine (30 microM), a compound which inhibits calcium release from intracellular stores, significantly inhibited the maximal contraction to carbamylcholine (3 microM). In contrast, ryanodine (30 microM) did not inhibit the maximal contraction to 5-HT (1 microM) in the absence of nitrendipine. However, ryanodine (30 microM) did significantly inhibit the nitrendipine-insensitive 5-HT contraction, suggesting that this component of the contraction was due in part to calcium release from a ryanodine-sensitive store. Bisindolylmaleimide (5 microM), a specific inhibitor of protein kinase C (PKC), inhibited 5-HT contraction in either the absence or presence of nitrendipine, suggesting that activation of PKC is also involved.(ABSTRACT TRUNCATED AT 250 WORDS)