Theophylline-Induced Relaxation Is Enhanced after Testosterone Treatment via Increased KV1.2 and KV1.5 Protein Expression in Guinea Pig Tracheal Smooth Muscle

Abstract

Theophylline is a drug commonly used to treat asthma due to its anti-inflammatory and bronchodilatory properties. Testosterone (TES) has been suggested to reduce the severity of asthma symptoms. This condition affects boys more than girls in childhood, and this ratio reverses at puberty. We reported that guinea pig tracheal tissue chronic exposure to TES increases the expression of β2-adrenoreceptors and enhances salbutamol-induced K+ currents (IK+). Herein, we investigated whether the upregulation of K+ channels can enhance the relaxation response to methylxanthines, including theophylline. Chronic incubation of guinea pig tracheas with TES (40 nM, 48 h) enhanced the relaxation induced by caffeine, isobutylmethylxanthine, and theophylline, an effect that was abolished by tetraethylammonium. In tracheal myocytes, chronic incubation with TES increased theophylline-induced IK+; flutamide reversed this effect. The increase in IK+ was blocked by 4-aminopyridine by ~82%, whereas iberiotoxin reduced IK+ by ~17%. Immunofluorescence studies showed that chronic TES exposure increased the expression of KV1.2 and KV1.5 in airway smooth muscle (ASM). In conclusion, chronic exposure to TES in guinea pig ASM promotes upregulation of KV1.2 and KV1.5 and enhances theophylline relaxation response. Therefore, gender should be considered when prescribing methylxanthines, as teenage boys and males are likely to respond better than females.

Testosterone Enhances KV Currents and Airway Smooth Muscle Relaxation Induced by ATP and UTP through P2Y4 Receptors and Adenylyl Cyclase Pathway

“…On the other hand, we recently demonstrated the genomic effects of TES on ASM relaxation. This androgen significantly augmented the relaxation caused by the clinically used bronchodilators, salbutamol and theophylline, in guinea pig tracheal rings by upregulating the β 2 -AR and K + channels [40,58,68]. In the experiments shown in the present work, a 48 h incubation of the androgen was performed, suggesting that the enhanced relaxation evoked by ATP and UTP may be due to a genomic pathway.…”

“…Previous immunofluorescence assays confirmed that the expression of two subtypes of KV, KV1.2 and KV1.5, in the ASM of guinea pigs increased when tracheal rings were exposed to 40 nM TES for 48 h (Figures 7 and 8) [58]. These results were analyzed by measurements of mean fluorescence intensity illustrated in Figures 7D and 8D.…”

“…SM stands for muscle, and EPI stands for epithelium. This immunofluorescence was taken from our previous work [58]. In control tracheal myocytes, the antagonist for almost all P2Y receptors except P2Y 2 , RB2 100 µM [59-62], partially decreased the K + currents induced by UTP (100 µM).…”

“…However, immunofluorescence experiments revealed that TES did not improve the expression of P2Y 4 receptors (Figure 10). This immunofluorescence was taken from our previous work [58].…”

“…In addition to Ca 2+ channels, K + channels play a primary role in regulating smooth muscle cells' membrane potential and excitability, influencing airway tone and contractility [27,56,57]. Our recent studies demonstrated that TES can directly modulate the expression of K V 1.5 and K V 1.2 in guinea pig ASM and enhance the relaxation response to salbutamol and theophylline via a genomic pathway [40,58]. Moreover, this androgen augments the expression of the β 2 adrenergic receptor (β 2 -AR) in the ASM [40].…”