Effectiveness of Columbianadin, a Bioactive Coumarin Derivative, in Perturbing Transient and Persistent I Na .

Columbianadin (CBN) is a bioactive coumarin-type compound with various biological activities. However, the action of CBN on the ionic mechanism remains largely uncertain, albeit it was reported to inhibit voltage-gated Ca ²⁺ current or to modulate TRP-channel activity. In this study, whole-cell patch-clamp current recordings were undertaken to explore the modifications of CBN or other related compounds on ionic currents in excitable cells (e.g., pituitary GH ₃ cells and HL-1 atrial cardiomyocytes). GH ₃ -cell exposure to CBN differentially decreased peak or late component of voltage-gated Na ⁺ current ( I _Na ) with effective IC ₅₀ of 14.7 or 2.8 µM, respectively. The inactivation time course of I _Na activated by short depolarization became fastened in the presence of CBN with estimated K _D value of 3.15 µM. The peak I _Na diminished by 10 µM CBN was further suppressed by subsequent addition of either sesamin (10 µM), ranolazine (10 µM), or tetrodotoxin (1 µM), but it was reversed by 10 µM tefluthrin (Tef); however, further application of 10 µM nimodipine failed to alter CBN-mediated inhibition of I _Na . CBN (10 µM) shifted the midpoint of inactivation curve of I _Na to the leftward direction. The CBN-mediated inhibition of peak I _Na exhibited tonic and use-dependent characteristics. Using triangular ramp pulse, the hysteresis of persistent I _Na enhanced by Tef was noticed, and the behavior was attenuated by subsequent addition of CBN. The delayed-rectifier or erg -mediated K ⁺ current was mildly inhibited by 10 µM CBN, while it also slightly inhibited the amplitude of hyperpolarization-activated cation current. In HL-1 atrial cardiomyocytes, CBN inhibited peak I _Na and raised the inactivation rate of the current; moreover, further application of 10 µM Tef attenuated CBN-mediated decrease in I _Na . Collectively, this study provides an important yet unidentified finding revealing that CBN modifies I _Na in electrically excitable cells.