Sphingosine increases inositol trisphosphate in rat parotid acinar cells by a mechanism that is independent of protein kinase C but dependent on extracellular calcium.
In rat parotid acinar cells prelabelled with [3H]-inositol, sphingosine stimulated the accumulation of [3H]-inositol polyphosphates. When the cells were exposed to sphingosine, [3H]-inositol trisphosphate (InsP3) was accumulated in a time- and dose-dependent manner. When the extracellular Ca2+ was chelated by 1 mM EGTA, the effect of sphingosine on InsP3 accumulation was completely inhibited. Ionophores, A23187 and ionomycin, had no significant effect on InsP3 accumulation. An inhibitor of protein kinase C, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), failed to stimulate InsP3 accumulation. In the homogenate of parotid acinar cells, InsP3 3-kinase and 5-phosphomonoesterase activities were not affected by sphingosine. These results suggest that sphingosine activates phosphoinositide turnover by a mechanism dependent upon extracellular Ca2+, but different from that of an ionophore, and independent of protein kinase C.
Sugiya
H
H
Department of Physiology, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
Furuyama
S
S
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D008297:Male; D010306:Parotid Gland / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013110:Sphingosine / Q000494:pharmacology*
D000001:Calcimycin; D015759:Ionomycin; D015544:Inositol 1,4,5-Trisphosphate; D011493:Protein Kinase C; D013110:Sphingosine; D002118:Calcium