Lysophospholipids regulate excitability and exocytosis in cultured bovine chromaffin cells

Bioactive lysophospholipids (LPLs) are released by blood cells and can modulate many cellular activities such as angiogenesis and cell survival. In this study, the effects of sphingosine-1-phosphate (S1P) and lysophosphatidic acid
(LPA) on excitability and exocytosis in bovine chromaffin cells were investigated using the whole-cell configuration of the patch-clamp. Voltage-gated Ca2+ current was inhibited by S1P and LPA pre-treatment in a concentration-dependent manner with IC50s of 0.46 and 0.79 lmol/L, respectively.
Inhibition was mostly reversible upon washout and prevented by suramin, an inhibitor of G-protein signaling. Na+ current was inhibited by S1P, but not by LPA. However, recovery of Na+ channels from inactivation was slowed by both LPLs. The outward K+ current was also significantly reduced by both
LPLs. Chromaffin cells fired repetitive action potentials in response to minimal injections of depolarizing current.Repetitive activity was dramatically reduced by LPLs. Consistent with the reduction in Ca2+ current, exocytosis elicited by a train of depolarizations and the ensuing endocytosis were both inhibited by LPL pre-treatments. These data demonstrate the interaction between immune and endocrine systems mediated by the inhibitory effects of LPLs on the excitability of adrenal chromaffin cells.