Purinergic signalling: therapeutic potential

El concepto de un sistema de señalización purinérgica, empleando los nucleótidos y nucleósidos de purina como mensajeros extracelulares, fue propuesto hace unos 30 años. Después de una breve introducción y puesta al día de los subtipos de receptores purinérgicos, este artículo se centra en los aspectos fisiopatológicos desempeñados por el ATP, ADP, UTP y adenosina. Estas moléculas median respuestas a corto plazo (agudas), como en la neurotransmisión, secreción y vasodilatación, y también respuestas a largo plazo (crónicas), como la señalización en el desarrollo, regeneración, proliferación y muerte celular. En condiciones patológicas, se observa que la expresión de los purinoceptores es muy versátil, incluyendo un incremento en el componente purinérgico del control nervioso parasimpático de la vejiga humana en el caso de sufrir cistitis intersticial y obstrucción del flujo, y también como cotransmisor en el control simpático de los vasos sanguíneos en ratas hipertensas. La acción antitrombótica del clopidogrel, un antagonista del receptor P2Y12, ha demostrado ser particularmente útil en la prevención de los infartos cerebrales recurrentes e infartos cardíacos en recientes ensayos clínicos. El papel del receptor P2X3 en la nocicepción y una nueva hipótesis sobre la transducción mecano-sensible en el dolor visceral, serán consideradas, así como el potencial terapéutico de los agonistas y antagonistas purinérgicos para el tratamiento de la taquicardia supraventricular, cáncer, ojo seco, hiperactividad de vejiga, disfunción eréctil, osteoporosis, diabetes, motilidad intestinal y anomalías respiratorias y vasculares

The concept of a purinergic signalling system, using purine nucleotides and nucleosides as extracellular messengers, was first proposed over 30 years ago. After a brief introduction and update of purinoceptor subtypes, this article focuses on the diverse pathophysiological roles of ATP, ADP, UTP and adenosine. These molecules mediate short-term (acute) signalling functions in neurotransmission, secretion and vasodilatation and long-term (chronic) signalling functions in development, regeneration, proliferation and cell death. Plasticity of purinoceptor expression in pathological conditions is frequently observed, including an increase in the purinergic component of parasympathetic nervous control of the human bladder in interstitial cystitis and outflow obstruction, and in sympathetic cotransmitter control of blood vessels in hypertensive rats. The antithrombotic action of clopidogrel, a P2Y12 receptor antagonist, has been shown to be particularly useful in the prevention of recurrent strokes and heart attacks in recent clinical trials. The role of P2X3 receptors in nociception and a novel hypothesis about purinergic mechano-sensory transduction in visceral pain will be considered, as well as the therapeutic potential of purinergic agonists or antagonists for the treatment of supraventricular tachycardia, cancer, dry eye, bladder hyperactivity, erectile dysfunction, osteoporosis, diabetes, gut motility, respiratory and vascular disorders

Participation of ATP in nonadrenergic, noncholinergic relaxation of longitudinal muscle of wistar rat jejunum.

A role of ATP in nonadrenergic, noncholinergic (NANC) relaxations was examined in the Wistar rat jejunum. Electrical field stimulation (EFS) induced NANC relaxation of longitudinal muscle of the jejunal segments in a frequency-dependent manner. A purinoceptor antagonist, adenosine 3'-phosphate 5'-phosphosulfate (A3P5PS, 100 muM) inhibited the relaxation: relaxations induced by EFS at lower or higher frequencies were either completely or partially inhibited, respectively. After the jejunal segments had been desensitized to ATP, the relaxations were decreased to the same extent as those inhibited by A3P5PS. An inhibitor of small conductance Ca(2+)-activated K(+) channels (SK channels), apamin (100 nM), completely inhibited EFS-induced relaxations. Treatment of the segments with an inhibitor of sarcoplasmic reticulum Ca(2+)-ATPase, thapsigargin (1 muM), significantly inhibited the relaxations. The exogenous ATP-induced relaxation of longitudinal muscle occurred with a concomitant decrease in intracellular Ca(2+) levels. Apamin and thapsigargin abolished these ATP-induced responses. A3P5PS significantly inhibited the inhibitory junction potentials which were induced in the longitudinal muscle cells. In addition, apamin significantly inhibited the hyperpolarization that was induced by exogenous ATP in the cells. These findings in the Wistar rat jejunum suggest that ATP participates in the NANC relaxation via activation of SK channels induced by Ca(2+) ions that are released from the thapsigargin-sensitive store site.