Modulation of high affinity ATP-dependent cyclic nucleotide transporters by specific and non-specific cyclic nucleotide phosphodiesterase inhibitors

Intracellular cyclic nucleotides are eliminated by phosphodiesterases (PDEs) and by ATP Binding cassette transporters such as ABCC4 and ABCC5. PDE5 and ABCC5 have similar affinity for cGMP whereas ABCC5 has much higher affinity for cGMP compared with cAMP. Since the substrate (cGMP) is identical for these two eliminatory processes it is conceivable that various PDE inhibitors also modulate ABCC5-transport. Cyclic GMP is also transported by ABBC4 but the affinity is much lower with a K-m 50-100 times higher than for that of ABBCC5. The present study aimed to determine K-i-values for specific or relative specific PDE5 inhibitors (vardenafil, tadalafil, zaprinast and dipyridamole) and the non-specific PDE inhibitors (IBMX, caffeine and theophylline) for ABCC5 andABCC4 transport. The transport of [H-3]-cGMP (2 mu M) was concentration-dependently inhibited with the following K-i-values: vardenafil (0.62 mu M), tadalatil (14.1 mu M), zaprinast (0.68 mu M) and dipyridamole (1.2 mu M), IBMX (10 mu M), caffeine (48 mu M) and theophylline (69 mu M). The K-i-values for the inhibition of the [H-3]-cAMP (2 mu M) transport were: vardenatil (3.4 mu M), tadalafil (194 mu M), zaprinast (2.8 mu M), clipyridamole (5.5 mu M), [BMX (16 mu M), caffeine (41 mu M) and theophylline (85 mu M). The specificity for ABCC5 we defined as ratio between K-i-values for inhibition at [H-3] -cAMP and [H-3]-cAMP transport. Tadalafil showed the highest specificity (K-i-ratio: 0.073) and caffeine the lowest (K-i-ratio: 1.2). (C) 2014 The Authors. Published by Elsevier B.V.