T- and L-type Ca2+ Currents in Freshly Dispersed Smooth Muscle Cells from the Human Proximal Urethra

The purpose of the present study was to characterise Ca2+ currents in smooth muscle cells isolated from biopsy samples taken from the proximal urethra of patients undergoing surgery for bladder or prostate cancer. Cells were studied at 37 °C using the amphotericin B perforated-patch configuration of the patch-clamp technique. Currents were recorded using Cs+-rich pipette solutions to block K+ currents. Two components of current, with electrophysiological and pharmacological properties typical of T- and L-type Ca2+ currents, were present in these cells. When steady-state inactivation curves for the L current were fitted with a Boltzmann equation, this yielded a V1/2 of −45 ± 5 mV. In contrast, the T current inactivated with a V1/2 of −80 ± 3 mV. The L currents were reduced in a concentration-dependent manner by nifedipine (ED50 = 159 ± 54 nm) and Ni2+ (ED50 = 65 ± 16 μm) but were enhanced when external Ca2+ was substituted with Ba2+. The T current was little affected by TTX, reduction in external Na+, application of nifedipine at concentrations below 300 nm or substitution of external Ca2+ with Ba2+, but was reduced by Ni2+ with an ED50 of 6 ± 1 μm. When cells were stepped from −100 to −30 mV in Ca2+-free conditions, small inward currents could be detected. These were enhanced 40-fold in divalent-cation-free solution and blocked in a concentration-dependent manner by Mg2+ with an ED50 of 32 ± 16 μm. These data support the idea that human urethral myocytes possess currents with electrophysiological and pharmacological properties typical of T- and L-type Ca2+ currents

Triathlon and Ultra-Endurance Events in Tropical Environments

International audiencePhysical performance in tropical environments, which combine heat and high humidity, is a challenge that requires specific preparation. The high humidity of a tropical climate alters thermoregulatory capacity by limiting the rate of sweat evaporation. Proper management of wholebody temperature is thus essential to complete an endurance event like a long-distance triathlon or an ultramarathon in such an environment. In triathlon and ultra-endurance races, which can last from 8 to 20 h, performance in tropical settings is closely linked to the capacity to maintain hydration status. Indeed, the rate of withdrawal in these longer events has been associated with water intake, with many finishers showing alterations in electrolyte (e.g. sodium) balance. To counterbalance the impact of a tropical climate and maintain performance, several countermeasures can be adopted, such as using hydration and cooling strategies, and heat acclimation