Testosterone Enhances K_V Currents and Airway Smooth Muscle Relaxation Induced by ATP and UTP through P2Y₄ Receptors...

Numerous studies suggest the involvement of adenosine-5'-triphosphate (ATP) and similar nucleotides in the pathophysiology of asthma. Androgens, such as testosterone (TES), are proposed to alleviate asthma symptoms in young men. ATP and uridine-5'-triphosphate (UTP) relax the airway smooth muscle (ASM) via purinergic P2Y₂ and P2Y₄ receptors and K⁺ channel opening. We previously demonstrated that TES increased the expression of voltage-dependent K⁺ (K_V) channels in ASM. This study investigates how TES may potentiate ASM relaxation induced by ATP and UTP. Tracheal tissues treated with or without TES (control group) from young male guinea pigs were used. In organ baths, tracheas exposed to TES (40 nM for 48 h) showed enhanced ATP- and UTP-evoked relaxation. Tetraethylammonium, a K⁺ channel blocker, annulled this effect. Patch-clamp experiments in tracheal myocytes showed that TES also increased ATP- and UTP-induced K⁺ currents, and this effect was abolished with flutamide (an androgen receptor antagonist). K_V channels were involved in this phenomenon, which was demonstrated by inhibition with 4-aminopyridine. RB2 (an antagonist of almost all P2Y receptors except for P2Y₂), as well as N-ethylmaleimide and SQ 22,536 (inhibitors of G proteins and adenylyl cyclase, respectively), attenuated the enhancement of the K⁺ currents induced by TES. Immunofluorescence and immunohistochemistry studies revealed that TES did not modify the expression of P2Y₄ receptors or COX-1 and COX-2, while we have demonstrated that this androgen augmented the expression of K_V1.2 and K_V1.5 channels in ASM. Thus, TES leads to the upregulation of P2Y₄ signaling and K_V channels in guinea pig ASM, enhancing ATP and UTP relaxation responses, which likely limits the severity of bronchospasm in young males.