Effects of tetraethylammonium‐sensitive K⁺ channel blockade on cholinergic and thermal sweating in endurance‐trained and untrained men

Abstract

We evaluated the hypothesis that the activation of K + channels mediates the exercisetraining-induced augmentation of cholinergic and thermal sweating. On separate days, 11 endurance-trained and 10 untrained men participated in two experimental protocols. Prior to each protocol, we administered 2% tetraethylammonium (TEA, K + channels blocker) and saline (Control) at forearm skin sites on both arms via transdermal iontophoresis. In protocol 1, low (0.001%) and high (1%) doses of pilocarpine were administered at the TEA-treated and Control sites over a 60-min period. In protocol 2, participants were passively heated by immersing their lower limbs in hot water (43 • C) until core (rectal) temperature (T c ) increased by 0.8 • C above resting levels. Administration of TEA attenuated cholinergic sweating (P = 0.001) during the initial 20 min after the treatment of low dose of pilocarpine only whilst the response was similar between the groups (P = 0.163). Cholinergic and thermal sweating were higher in the trained relative to the untrained men (all P ≤ 0.033). Thermal sweating reached ∼90% of the response at a T c elevation of 0.8 • C during the initial 20 min of passive heating, which corresponds to the period wherein TEA attenuated cholinergic sweating in protocol 1. However, sweating did not differ between the Control and TEA sites in either group (P = 0.704). We showed that activation of K + channels does not appear to mediate the elevated sweating response induced by a low dose of pilocarpine in trained men. We also demonstrated that K + channels do not contribute to sweating during heat stress in either group.