Phosphoinositides in frog skeletal muscle: a quantitative analysis.
The contents of major phospholipids per g of wet wt. in frog skeletal muscle are: 5.3 mumol PC; 1.4 mumol PE; 1 mumol SM; 0.4 mumol PtdIns; 0.3 mumol CL; and 0.13 mumol PS. The quantities of polyphosphoinositides per g of wet wt. are: 181 nmol PtInsP; 28 nmol PtdInsP2; and 8 nmol lyso-PtdInsP2. The specific activity of labelling of the total muscle ATP attained by external incubation with [32P]Pi was found to be 57 dpm/nmol x g muscle wet wt. PtdInsP2, the highest labelled polyphosphoinositide, showed a specific activity of 64,000 dpm/nmol per g muscle wet wt., suggesting that high specific activity ATP may be compartmentalized in the local environment of the triads and used as a substrate by the PtdIns and PtInsP kinase in that region. PtdInsP2 which is the immediate precursor for the release of InsP3, is found at a significant concentration and strategically located for its postulated role as a substrate for the action of phosphoinositidase C. The presence of a novel endogenous polyphosphoinositide, lyso-PtdInsP2, in animal tissues is reported for the first time. Electrical stimulation leads towards a rapid catabolization of polyphosphoinositides revealed by reductions in the 3H- and 32P-labelling, suggesting that muscle excitation is associated with the activation of breaking down of polyphosphoinositides.
Lagos
N
N
Department of Physiology, School of Medicine, University of California, Los Angeles 90024-1751.
Vergara
J
J
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D004558:Electric Stimulation; D007294:Inositol / Q000378:metabolism; D008246:Lysophospholipids / Q000378:metabolism; D009132:Muscles / Q000032:analysis* / Q000201:enzymology / Q000502:physiology; D010716:Phosphatidylinositols / Q000032:analysis*; D010741:Phospholipases A / Q000378:metabolism; D011892:Rana catesbeiana
D008246:Lysophospholipids; D010716:Phosphatidylinositols; D007294:Inositol; D010741:Phospholipases A