Sildenafil decreases rat tracheal hyperresponsiveness to carbachol and changes canonical transient receptor potential gene expression after antigen challenge

Inhibition of type-5 phosphodiesterase by sildenafil decreases capacitative Ca2+ entry mediated by transient receptor potential proteins (TRPs) in the pulmonary artery. These families of channels, especially the canonical TRP (TRPC) subfamily, may be involved in the development of bronchial hyperresponsiveness, a hallmark of asthma. In the present study, we evaluated i) the effects of sildenafil on tracheal rings of rats subjected to antigen challenge, ii) whether the extent of TRPC gene expression may be modified by antigen challenge, and iii) whether inhibition of type-5 phosphodiesterase (PDE5) may alter TRPC gene expression after antigen challenge. Sildenafil (0.1 µM to 0.6 mM) fully relaxed carbachol-induced contractions in isolated tracheal rings prepared from naive male Wistar rats (250-300 g) by activating the NO-cGMP-K+ channel pathway. Rats sensitized to antigen by intraperitoneal injections of ovalbumin were subjected to antigen challenge by ovalbumin inhalation, and their tracheal rings were used to study the effects of sildenafil, which more effectively inhibited contractions induced by either carbachol (10 µM) or extracellular Ca2+ restoration after thapsigargin (1 µM) treatment. Antigen challenge increased the expression of the TRPC1 and TRPC4 genes but not the expression of the TRPC5 and TRPC6 genes. Applied before the antigen challenge, sildenafil increased the gene expression, which was evaluated by RT-PCR, of TRPC1 and TRPC6, decreased TRPC5 expression, and was inert against TRPC4. Thus, we conclude that PDE5 inhibition is involved in the development of an airway hyperresponsive phenotype in rats after antigen challenge by altering TRPC gene expression.

Capacitative Ca~(2+) entry mediate contraction in rat distal colon smooth muscle / 中国药理学通报

Aim To investigate whether capacitative Ca~(2+) entry involved in excitation-contraction coupling in rat distal colon smooth muscle.Methods Changes of isolated organ's tension were monitored with force-displacement transducer and Powerlab 4/25T recording system.Results Thapsigargin(10 nmol?L~(-1)～1 ?mol?L~(-1))produced slowly developing sustained contractions in isolated distal colon smooth muscle strips of rats.The timed contractile responses to thapsigargin(10 n mol?L~(1)-1 ?mol?L~(-1)) were significantly different.The contractile response to Ca~(2+) reintroduction following incubation of strips in a Ca~(2+)-free Krebs in the presense of thapsigargin was significantly higher than in its absence(99%?28% vs 70%?8%).Contractile responses to Ca~(2+)reintroduction following depletion of sarcoplasmic reticulum Ca~(2+) stores with thapsigargin were attenuated by La~(3+),while unaffected by verapamil.Conclusion Contractile responses to Ca~(2+)reintroduction following depletion of sarcoplasmic reticulum Ca~(2+)stores with thapsigargin,are mediated by capacitative Ca~(2+)entry.The results suggested that CCE provided activator Ca~(2+)for the contraction and participated in excitation-contraction process in rat distal colon smooth muscle.