Regulation of human cardiac Kv1.5 channels by extracellular acidification

The inhibitory effects of levo-tetrahydropalmatine on rat Kv1.5 channels expressed in HEK293 cells

Levo-tetrahydropalmatine (l-THP) exerts various pharmacological effects on neural and cardiac tissues and K⁺ channel can be one of its multiple targets. The rapidly activating Kv1.5 channel is expressed in a variety of tissues including atrial cells and hippocampal neurons, and has an essential role in tuning the action potential and excitability in those cells. The aim of current study is to explore whether there are the possible effects of l-THP on Kv1.5 channels expressed in HEK293 cells. Superfusion of l-THP led to a dose-dependent blockage of Kv1.5 currents with an IC₅₀ value of 53.2μM. This blocking effect was substantially attenuated in mutant H452G rather than R476V and R476Y, suggesting a specific binding site in the outer mouth region. In addition, the properties of Kv1.5 channel kinetics were markedly altered by l-THP. Treatment with l-THP resulted in a potential left shift of the inactivation curve, with the half-maximum inactivation potential (V_1/2) of 4.5mV in control and -12.8mV in 50μM l-THP. Our data reveal that l-THP can exert an inhibitory effect on the delayed rectifier Kv1.5 channels expressed in HEK293 cells. These lines of evidence provided an insight to understand the possible effects exerted by l-THP on relative tissues.