Curine, a bisbenzylisoquinoline alkaloid, blocks L-type Ca2+ channels and decreases intracellular Ca2+ transients in A7r5 cells

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Curine is a novel bisbenzylisoquinoline alkaloid that has previously been reported as a vasodilator. The underlying mechanism(s) of the vasodilator effect of curine remains to be characterized. In this study, we investigated the cellular mechanism that is responsible for the vasodilator effect of curine in the rat aorta. The vasorelaxant activity of curine was recorded using a myograph. Ca2+ currents in A7r5 cells were measured using the whole-cell patch-clamp technique. Intracellular Ca2+ transients were determined using confocal microscopy. In a concentration-dependent manner, curine inhibited contractions elicited by high extracellular K+ and Bay K8644 in the rat aorta and reduced the rise in the intracellular Ca2+ concentration induced by membrane depolarization in response to an increase in extracellular K+ concentration in vascular smooth muscle cells. Moreover, curine decreased the peak amplitude of L-type Ca2+ currents (ICa,L) in a concentration-dependent manner without changing the characteristics of the current density vs. voltage relationship and the steady-state activation of ICa,L. Furthermore, curine shifted the steady-state inactivation curve of ICa,L toward more hyperpolarized membrane potentials. None of the following modified the effect of curine on ICa,L amplitude: 3-isobutyl-1-methylxanthine, an inhibitor of phosphodiesterases; dibutyryl cyclic AMP, an activator of protein kinase A (PKA); or 8-Br-cyclic GMP, an activator of protein kinase G (PKG). Our results showed that curine inhibited the L-type voltage-dependent Ca2+ current in rat aorta smooth muscle cells, which caused a decrease in intracellular global Ca2+ transients that led to vasorelaxation.

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