Sphingosine-1-phosphate activates BK_Ca channels independently of G protein-coupled receptor in human endothelial cells

Abstract

The effect of sphingosine-1-phosphate (S1P) on large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels was examined in primary cultured human umbilical vein endothelial cells by measuring intracellular Ca(2+) concentration ([Ca(2+)](i)), whole cell membrane currents, and single-channel activity. In nystatin-perforated current-clamped cells, S1P hyperpolarized the membrane and simultaneously increased [Ca(2+)](i). [Ca(2+)](i) and membrane potentials were strongly correlated. In whole cell clamped cells, BK(Ca) currents were activated by increasing [Ca(2+)](i) via cell dialysis with pipette solution, and the activated BK(Ca) currents were further enhanced by S1P. When [Ca(2+)](i) was buffered at 1 microM, the S1P concentration required to evoke half-maximal activation was 403 +/- 13 nM. In inside-out patches, when S1P was included in the bath solution, S1P enhanced BK(Ca) channel activity in a reversible manner and shifted the relationship between Ca(2+) concentration in the bath solution and the mean open probability to the left. In whole cell clamped cells or inside-out patches loaded with guanosine 5'-O-(2-thiodiphosphate) (GDPbetaS; 1 mM) using a patch pipette, GDPbetaS application or pretreatment of cells with pertussis toxin (100 ng/ml) for 15 h did not affect S1P-induced BK(Ca) current and channel activation. These results suggest that S1P enhances BK(Ca) channel activity by increasing Ca(2+) sensitivity. This channel activation hyperpolarizes the membrane and thereby increases Ca(2+) influx through Ca(2+) entry channels. Inasmuch as S1P activates BK(Ca) channels via a mechanism independent of G protein-coupled receptors, S1P may be a component of the intracellular second messenger that is involved in Ca(2+) mobilization in human endothelial cells.

Oxidized Low-density Lipoprotein- and Lysophosphatidylcholine-induced Ca2+ Mobilization in Human Endothelial Cells

“…In addition, OxLDL or LPC might increase the sensitivity of BKCa channels to Ca 2＋ , because OxLDL or LPC augmented BKCa current further which was already activated by clamping [Ca 2＋ ]i to 1 μM. BKCa current activation can hyperpolarize membrane, thereby increasing the driving force for Ca 2＋ Kim et al, 2006 ]i. These effects of OxLDL on HUVECs are mimicked by its main lipid constituent LPC, and therefore, LPC mediates these responses on endothelial cells.…”

Recruitment of sphingosine kinase to presynaptic terminals by a conserved muscarinic signaling pathway promotes neurotransmitter release

“…In addition, S1P generated in muscles may be able to diffuse to motor neurons, but likely acts by a mechanism independent of known S1P receptors. S1P can interact with multiple intracellular targets, including transient receptor potential (TRP) channels, store-operated calcium channels, inositol triphosphate receptors, and calcium-activated potassium channels (BK Ca ) (Ghosh et al 1994;Mattie et al 1994;Flemming et al 2006;Kim et al 2006). Although these targets are found in neurons, the functional significance of their interaction with S1P on neurotransmitter release is not known.…”

S1P1 Receptor Modulation Preserves Vascular Function in Mesenteric and Coronary Arteries after CPB in the Rat Independent of Depletion of Lymphocytes

“…However, other studies found the involvement of S1P1 receptors in the regulation of contractile reactivity [44]–[47] and S1P agonist were found recently to evoke vasoconstriction of the afferent renal arterioles via S1P1 and S1P2 receptors with involvement of the L-type voltage-dependent calcium channels [48]. Further, S1P induces COX-2 expression in vascular smooth muscle cells, which seems partially mediated via S1P1 receptors [49].…”

“…The comparable effect of both FTY720 and SEW2871 on vascular contractility suggests the involvement of S1P 1 receptor-dependent mechanism, whereas vascular smooth muscle were reported to express mainly S1P2 and S1P3 receptors that mediate vasoconstriction [40]–[43] through activation of the phospholipase C, myosin light chain kinase and/or Rho-associated kinase-dependent inhibition of myosin light chain phosphatase [44]–[47]. However, other studies found the involvement of S1P1 receptors in the regulation of contractile reactivity [44]–[47] and S1P agonist were found recently to evoke vasoconstriction of the afferent renal arterioles via S1P1 and S1P2 receptors with involvement of the L-type voltage-dependent calcium channels [48].…”