Effects of L-type voltage-gated Ca2+ channel blockade on cholinergic and thermal sweating in habitually trained and untrained men.

We evaluated the hypothesis that the activation of L-type voltage-gated Ca2+ channels contribute to exercise training-induced augmentation in cholinergic sweating. On separate days, 10 habitually trained and 10 untrained men participated in two experimental protocols. Prior to each protocol, we administered 1% verapamil (Verapamil, L-type voltage-gated Ca2+ channel blocker) and saline (Control) at forearm skin sites on both arms via transdermal iontophoresis. In Protocol 1, we administered low (0.001%) and high (1%) doses of pilocarpine at both the verapamil-treated and untreated forearm sites. In protocol 2, participants were passively heated by immersing their limbs in hot water (43°C) until rectal temperature increased by 1.0°C above baseline resting levels. Sweat rate at all forearm sites were continuously measured throughout both protocols. Pilocarpine-induced sweating in Control was higher in trained than in untrained men for both concentrations of pilocarpine (both P≤0.001). Pilocarpine-induced sweating at the low dose site was attenuated at the Verapamil versus Control site in both groups (both P≤0.004), albeit the reduction was greater in trained as compared to untrained men (P=0.005). The verapamil-mediated reduction in sweating remained intact at the high dose pilocarpine site in the untrained (P=0.004) but not the trained men (P=0.180). Sweating did not differ between Control and Verapamil sites with increases in rectal temperature in both groups (interaction, P=0.571). We show that activation of L-type voltage-gated Ca2+ channels modulates sweat production in habitually trained men induced by a low dose of pilocarpine. However, no effect on sweating was observed during passive heating in either group.