title: PPADS, a P2X receptor antagonist, as a novel inhibitor of the reverse mode of the Na⁺/Ca²⁺ exchanger in guinea pig airway smooth muscle.
abstract: The Na(+)/Ca(2+)exchanger (NCX) principal function is taking 1 Ca(2+) out of the cytoplasm and introducing 3 Na(+). The increase of cytoplasmic Na(+) concentration induces the NCX reverse mode (NCX(REV)), favoring Ca(2+) influx. NCX(REV) can be inhibited by: KB-R7943 a non-specific compound that blocks voltage-dependent and store-operated Ca(2+) channels; SEA0400 that appears to be selective for NCX(REV), but difficult to obtain and SN-6, which efficacy has been shown only in cardiomyocytes. We found that PPADS, a P2X receptor antagonist, acts as a NCX(REV) inhibitor in guinea pig tracheal myocytes. In these cells, we characterized the NCX(REV) by substituting NaCl and NaHCO(3) with LiCl, resulting in the increase of the intracellular Ca(2+) concentration ([Ca(2+)]i) using fura 2-AM. We analyzed 5 consecutive responses of the NCX(REV) every 10 min, finding no differences among them. To evaluate the effect of different NCX(REV) blockers, concentration response curves to KB-R7943 (1, 3.2 and 10 μM), and SN-6 (3.2, 10 and 30 μM) were constructed, whereas PPADS effect was characterized as time- and concentration-dependent (1, 3.2, 10 and 30 μM). PPADS had similar potency and efficacy as KB-R7943, whereas SN-6 was the least effective. Furthermore, KCl-induced contraction, sensitive to D600 and nifedipine, was blocked by KB-R7943, but not by PPADS. KCl-induced [Ca(2+)]i increment in myocytes was also significantly decreased by KBR-7943 (10 μM). Our results demonstrate that PPADS can be used as a reliable pharmacological tool to inhibit NCX(REV), with the advantage that it is more specific than KB-R7943 because it does not affect L-type Ca(2+) channels.
authors: Departamento de Farmacología, Facultad de Medicina, Universidad Nacional Autónoma de México, México DF, Mexico.
authors: Edgar
authors: E
authors: Flores-Soto
authors: Jorge
authors: J
authors: Reyes-García
authors: Bettina
authors: B
authors: Sommer
authors: Jaime
authors: J
authors: Chavez
authors: Carlos
authors: C
authors: Barajas-López
authors: Luis M
authors: LM
authors: Montaño
mesh_terms: D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism; D006168:Guinea Pigs; D008297:Male; D032342:Muscle Cells / Q000187:drug effects / Q000378:metabolism; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D058920:Purinergic P2X Receptor Antagonists / Q000494:pharmacology*; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D058469:Receptors, Purinergic P2X / Q000378:metabolism*; D015203:Reproducibility of Results; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors*; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology; D014132:Trachea / Q000166:cytology*
chemical_list: C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D058920:Purinergic P2X Receptor Antagonists; D058469:Receptors, Purinergic P2X; D019831:Sodium-Calcium Exchanger; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; D011732:Pyridoxal Phosphate; D013890:Thiourea