ATP Evokes Inward Currents in Corpus Cavernosum Myocytes. (24th October 2013) - Doyle, Claire
Abstract Introduction Although adenosine triphosphate (ATP) has often been reported to relax the corpus cavernosum, this may be mediated by indirect effects, such as release of nitric oxide from the endothelium. Recent data suggest that P2X1 receptors may be up‐regulated in diabetes, and these exert an anti‐erectile effect by causing the corpus cavernosum smooth muscle cells (CCSMCs) to contract. However, to date, there is no functional evidence that ATP can directly stimulate CCSMC. Aims This study aims to (i) to directly examine the effect of ATP on membrane currents in freshly isolated CCSMC, where influences of endothelium and other cells are absent; and (ii) to determine the receptor subtypes, ionic currents, and Ca2+ signals stimulated by ATP. Methods CCSMCs were enzymatically dispersed from male New Zealand White rabbits for patch clamp recording and measurement of intracellular Ca2+ in fluo‐4‐loaded cells using spinning disk confocal microscopy. Main Outcome Measures Patch clamp recordings were made of ATP‐evoked membrane currents and spontaneous membrane currents. Spinning disk confocal imaging of intracellular Ca2+ was performed, and the response to ATP was recorded. Results ATP evoked repeatable inward currents in CCSMC (1st application: −675 ± 101 pA; 2nd application: −694 ± 120 pA, N = 9, P = 0.77). ATP‐induced currents were reduced by suramin from −380 ± 121 to −124 ± 37 pA (N = 8, P < 0.05), by α, β‐methylene ATP from −755 ± 235 to 139 ± 49 pA (N = 5, P < 0.05), and by NF449 from −419 ± to −51 ± 13 pA (N = 6, P < 0.05). In contrast, MRS2500, a P2Y1 antagonist, had no effect on ATP responses (control: −838 ± 139 pA; in MRS2500: −822 ± 184 pA, N = 13, P = 0.84) but blocked inward currents evoked by 2‐MeSATP, a P2Y1, 12, 13 agonist (control: −623 ± 166 pA; in MRS2500: −56 ± 25 pA, N = 6, P < 0.05). The ATP‐evoked inward current was unaffected by changing the transmembrane Cl− gradient but reversed in direction when extracellular Na+ was reduced, indicating that it was a cation current. Conclusions ATP directly stimulates CCSMC by evoking a P2X‐mediated cation current. Doyle C, Sergeant GP, Hollywood MA, McHale NG, and Thornbury KD. ATP evokes inward currents in corpus cavernosum myocytes. J Sex Med 2014;11:64–74.