Guanine nucleotide-sensitive inhibition of L-type Ca2+ current by lysosphingolipids in RINm5F insulinoma cells.
The lysosphingolipids sphingosine-1-phosphate (SPP) and sphingosylphosphorylcholine (SPPC) reportedly increase free cytosolic Ca2+ concentration ([Ca2+]i) in a variety of cell types, apparently by activating G protein-coupled plasma membrane receptors. We investigated whether and how sphingolipids modulate Ca2+ homeostasis in the insulinoma cell line RINm5F. The addition of SPPC and glucopsychosine (GPS) did not affect basal [Ca2+]i but inhibited the KCl (30 mM)-induced increase in [Ca2+]i in a pertussis toxin-insensitive and concentration-dependent manner (EC50 approximately 5 micro M). Similar inhibitory effects were observed with dihydro-SPPC and psychosine, whereas SPP and various N-acylated sphingolipids (at 10 micro M each) had little or no effect on the KCl-induced [Ca2+]i increase. Because in RINm5F cells the primary pathway for depolarization-induced [Ca2+]i increase are L-type Ca2+ channels, we studied whether sphingolipids reduce L-type Ca2+ current (ICa.L). When added to the bath, GPS and SPPC, but not SPP (10 micro M each), rapidly reduced maximal ICa.L by approximately 35%, similar to the alpha2-adrenoceptor agonist clonidine (30 micro M). However, when applied internally, GPS had no effect on ICa. L. When the electrode solution contained the stable GDP analog guanosine-5'-O-(2-thio)diphosphate (1 and 10 mM), the inhibitory effect of GPS was abolished. In conclusion, a novel cellular action of lysosphingolipids is observed in RINm5F cells (i.e., a guanine nucleotide-sensitive inhibition of L-type Ca2+ currents). The pharmacological profile of this inhibition is unique and unlike any known lysosphingolipid receptor-mediated action.
Himmel
H M
HM
Institut für Pharmakologie, Universitätsklinikum Essen, D-45122 Essen, Germany.
Meyer zu Heringdorf
D
D
Windorfer
B
B
van Koppen
C J
CJ
Ravens
U
U
Jakobs
K H
KH
D001464:Barium / Q000037:antagonists & inhibitors; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects*; D020746:Calcium Channels, L-Type; D002460:Cell Line; D006150:Guanine Nucleotides / Q000494:pharmacology*; D006801:Humans; D007340:Insulinoma / Q000378:metabolism / Q000473:pathology; D008246:Lysophospholipids; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D018340:Receptors, Adrenergic, alpha-1 / Q000235:genetics; D011943:Receptors, Adrenergic, beta / Q000235:genetics; D022702:Receptors, Adrenergic, beta-3; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D006150:Guanine Nucleotides; D008246:Lysophospholipids; D018340:Receptors, Adrenergic, alpha-1; D011943:Receptors, Adrenergic, beta; D022702:Receptors, Adrenergic, beta-3; C005356:sphingosine phosphorylcholine; D010767:Phosphorylcholine; D001464:Barium; C060506:sphingosine 1-phosphate; D011189:Potassium Chloride; D013110:Sphingosine; D002118:Calcium