Effect of heat shock, [Ca2+]i, and cAMP on inositol trisphosphate in human epidermoid A-431 cells.
The basal levels of inositol monophosphate, inositol bisphosphate, and inositol trisphosphate (InsP3) in A-431 cells incubated in Na(+)-Hanks' solution were, respectively, 1.23 +/- 0.18, 0.17 +/- 0.03, and 0.69 +/- 0.07% of the total radioactivity in the cell. When cells were heated, InsP3 increased in a temperature-dependent manner related to the duration of heating. The active form of InsP3, inositol 1,4,5-trisphosphate, increased 237 +/- 17% after heating (45 degrees C, 20 min) then returned to baseline within 15 min after the return to 37 degrees C. The heat-induced increase in InsP3 was not observed in the absence of extracellular Ca2+ or with amiloride treatment. Treatment with the nonhydrolyzable GTP analogue 5'-guanylylimidodiphosphate stimulated that component of the InsP3 increase due to G proteins. U-73122, an inhibitor of phospholipase C-mediated processes, blocked the increase in InsP3 resulting from heat exposure. Both pertussis toxin (30 ng/ml, 24 h), an inhibitor of G inhibitory protein, and cholera toxin (1 microgram/ml, 1 h), a stimulator of G stimulatory protein, increased InsP3 in unheated cells, and heating failed to induce a further increase, suggesting that heat activates G proteins. Likewise, 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP), 3-isobutyl-1-methylxanthine, Ro 20-1724, or forskolin increased InsP3 in unheated cells, and heat did not cause an additional increase. The InsP3 increase induced by 8-BrcAMP was inhibited by removal of extracellular Ca2+ or treatment with verapamil, suggesting that an influx of extracellular Ca2+ stimulates InsP3 production.(ABSTRACT TRUNCATED AT 250 WORDS)
Kiang
J G
JG
Department of Clinical Physiology, Walter Reed Army Institute of Research, Washington, District of Columbia 20307-5100.
McClain
D E
DE
D000143:Acids / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002294:Carcinoma, Squamous Cell / Q000378:metabolism* / Q000473:pathology; D000242:Cyclic AMP / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000502:physiology; D006358:Hot Temperature; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism*; D009994:Osmolar Concentration; D012769:Shock / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000494:pharmacology
D000143:Acids; D015544:Inositol 1,4,5-Trisphosphate; D000242:Cyclic AMP; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D002118:Calcium