Effects of the phospholipid environment in the plasma membrane on receptor interaction with the adenylyl cyclase complex of intact cells.

A1 Journal article (refereed)


Internal Authors/Editors


Publication Details

List of Authors: Christian Jansson, Ann-Sofi Härmälä, Diana M. Toivola, Peter Slotte
Publisher: ELSEVIER SCIENCE BV
Publication year: 1993
Journal: BBA - Biochimica et Biophysica Acta
Journal acronym: BIOCHIM BIOPHYS ACTA
Volume number: 1145
Issue number: 2
Start page: 311
End page: 319
Number of pages: 9
ISSN: 0006-3002


Abstract

In this study we have examined the effects of variations of the plasma membrane phospholipid and cholesterol content on the metabolic functions of the adenylyl cyclase complex in intact cells. Exposure of cells to 0.1 U/ml of sphingomyelinase led to the degradation of 75, 55 and 40% of the cellular total sphingomyelin mass in human skin fibroblasts (HSF), Chinese hamster lung fibroblasts (CHLF) and rat liver hepatocytes (RLH), respectively. Degradation of sphingomyelin in native cells led in turn to a reduction (within 60 min) of the plasma membrane cholesterol content (by 25, 15 and 10%, respectively). This manipulation of the plasma membrane lipid content did not affect the forskolin or prostaglandin E1-induced activation of adenylyl cyclase (as measured from the conversion of [H-3]adenine via [H-3]ATP to [H-3]cAMP). These manipulations did, however, increase the basal rate of [H-3]cAMP formation in rat liver hepatocytes (but not in the fibroblast cell types). With Chinese hamster lung fibroblasts, transfected to express an alpha2-adrenergic receptor, it was observed that the alpha2-adrenergic receptor-induced inhibition of adenylyl cyclase activity was slightly (but significantly) diminished in sphingomyelin and cholesterol-depleted cells. With isolated rat liver hepatocytes it was observed that the glucagon (receptor) mediated activation of adenylyl cyclase was also reduced in sphingomyelinase-treated cells. In another set of experiments, CHLF and RLH cells were exposed for 2 h to vesicles prepared from dilauroylphosphatidylcholine, to increase the lateral packing density in the outer leaflet of the plasma membrane. In such treated cells, the receptor-coupling to adenylyl cyclase was markedly reduced both in CHLF (the alpha2-adrenergic receptor) and RLH (the glucagon-receptor) cells. We conclude that the direct activation of adenylyl cyclase (i.e., by forskolin) is not markedly affected by manipulations outer leaflet phospholipid composition (either reduction of sphingomyelin or increase of phosphatidylcholine), whereas receptor-coupled events clearly are.


Keywords

ADENYLYL CYCLASE COMPLEX, alpha(2)-adrenergic receptor, CYCLIC AMP, (FIBROBLAST)

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