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Campos-Toimil M, Keravis T, Orallo F, Takeda K, Lugnier C: Short-term or long-term treatments with a phosphodiesterase-4 (PDE4) inhibitor result in opposing agonist-induced Ca (2+) responses in endothelial cells. Br J Pharmacol. 2008 May;154(1):82-92. Epub 2008 Mar 3.
BACKGROUND AND PURPOSE: We previously reported that agonist-induced rises in cytoplasmic Ca (2+) concentration ([Ca (2+)](i)) in human umbilical vein endothelial cells (HUVEC) were inhibited after a short-term (2 min) pre-treatment with cAMP-elevating agents. The aim of this work was to study the effects of longer term (8 h) pre-treatment with dibutyryl-cAMP (db-cAMP) or rolipram, a specific inhibitor of phosphodiesterase-4 (PDE4), on [Ca (2+)](i), cAMP levels and PDE activity and expression in HUVEC. EXPERIMENTAL APPROACH: [Ca (2+)](i) changes were measured in isolated HUVEC by Fura-2 imaging. Intracellular cAMP levels and PDE4 activity were assessed by enzyme-immunoassay and radio-enzymatic assay, respectively. PDE expression was measured by northern and western blot analysis. KEY RESULTS: Long-term pre-treatment of HUVEC with rolipram or db-cAMP significantly increased ATP-, histamine- and thrombin-induced [Ca (2+)](i) rises. Short-term pre-treatment with rolipram was associated with an increase in cAMP, whereas long-term pre-treatment was associated with a decrease in cAMP. Long-term pre-treatment with rolipram or db-cAMP induced a significant increase in PDE4 activity and the expression of 74 kDa-PDE4A and 73 kDa-PDE4B was specifically enhanced. All these effects were suppressed by cycloheximide. CONCLUSIONS AND IMPLICATIONS: Our data suggest that sustained inhibition of PDE4 by rolipram induced an increase in PDE4 activity, possibly as a compensatory mechanism to accelerate cAMP degradation and that PDE4A and PDE4B were implicated in the regulation of [Ca (2+)](i). Thus, isozyme-specific PDE4 inhibitors might be useful as therapeutic agents in diseases where [Ca (2+)](i) handling is altered, such as atherosclerosis, hypertension and tolerance to beta-adrenoceptor agonists. |
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