G protein-coupled receptors (GPCRs) 1 constitute the main class of membrane receptors and form the widest gene family known in the mammalian genome. Therefore, signal transduction via G proteins represents one of the most important ways of cell signaling (for a review, see Ref. 1). Upon activation by agonists, GPCRs undergo conformational changes that induce the activation of heterotrimeric G proteins, promoting the exchange of the GDP bound to the G␣ subunit for GTP. This exchange provokes the dissociation of the G␣ subunit from the G␤␥ dimer and enables both molecular entities to modulate the activity of specific effectors or other signaling proteins (e.g. G protein receptor kinases).The association of both GPCRs and G proteins to the plasma membrane makes them susceptible to their lipid environment so that lipid-protein interactions are crucial to their function. In recent years, evidence has accumulated showing that the plasma membrane organization is more complex than a simple "chaotic sea" of bipolar lipid molecules in a liquid-crystalline state that only serves to support membrane proteins (2). In fact, differentiated membrane domains with specific protein and lipid compositions can exist in a cell such as the basal and apical membranes of epithelial/endothelial cells, the pre-and postsynaptic membranes of neuronal synapses, or lipid rafts and caveolae. Moreover, the extracellular and cytosolic leaflets of the plasma membrane differ in their lipid composition (3), further demonstrating the relevance of lipids in the organization and function of the membrane. Natural membranes are composed of different amphitropic molecules that differ in their propensity to form secondary lipid structures that influence the structural properties of the membrane (for a review, see Ref. 4). In this context, hexagonal (H II ) structures regulate the localization and activity of some key membrane signaling proteins (5, 6). Indeed, we have recently been able to show that changes in the lipid composition of erythrocyte cell membranes can influence the membrane association of G proteins and protein kinase C in vivo (7). Moreover, the neural membranes of cold-adapted fishes contain higher levels of phosphatidylethanolamine (PE) species in winter than in summer (8). These lipid changes probably lower the solidto-liquid and lamellar-to-hexagonal phase transition temperatures of membranes to maintain protein function and cell signaling in neurons and other cells. These data suggest that hexagonal phase propensity plays a major role in regulating physiological processes and might also participate in the control of other pivotal cellular events influenced by membrane proteins, such as cell growth or energy metabolism.Our main goal was to elucidate the role of the membrane lipid structure in the association to membranes of heterotrimeric G proteins and the molecular entities formed after their receptor-mediated activation. For this purpose we used synthetic membranes (liposomes) and purified G proteins as model systems because their li...

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Summary Using a highly sensitive immunofluorometric procedure, we measured the total prostate-specific antigen (PSA) concentration in 632 sera obtained from female blood donors and women with idiopathic hirsutism, breast cancer or benign breast diseases. A total of 50 sera with total PSA> 15 ng 1-' were fractionated by high-performance liquid chromatography (HPLC) in order to resolve the two immunoreactive molecular forms, i.e. free PSA (approximately 30 kDa) and PSA bound to a1-antichymotrypsin (PSA-ACT, 100 kDa). We found that breast cancer patients have presurgical serum total PSA levels similar to those of blood donors. Total serum PSA concentration decreases with age in women with idiopathic hirsutism, in cancer patients and in patients with benign breast diseases. The major molecular form of PSA in the serum of all normal and hirsute women (n = 15) is PSA bound to the proteinase inhibitor a,-antichymotrypsin. The major molecular form in 44% of presurgical cancer patient sera-is free PSA. A total of 58% of benign breast disease patients also have in their serum mainly free PSA. We conclude that about half the patients with breast cancer or benign breast diseases have free PSA as the major molecular form in their serum, whereas patients without breast pathologies (normal blood donors, idiopathic hirsutism) have PSA bound to a1-antichymotrypsin as the major molecular form. The ratio of PSA/PSA-ACT may have value as a simple biochemical test for diagnosis of breast pathologies including breast cancer.

Chronic hypoxia protects the heart against injury caused by acute oxygen deprivation, but its salutary mechanism is poorly understood. The aim was to find out whether cardiomyocytes isolated from chronically hypoxic hearts retain the improved resistance to injury and whether the mitochondrial large-conductance Ca2+-activated K+ (BKCa) channels contribute to the protective effect. Adult male rats were adapted to continuous normobaric hypoxia (inspired O2 fraction 0.10) for 3 wk or kept at room air (normoxic controls). Myocytes, isolated separately from the left ventricle (LVM), septum (SEPM), and right ventricle, were exposed to 25-min metabolic inhibition with sodium cyanide, followed by 30-min reenergization (MI/R). Some LVM were treated with either 30 μM NS-1619 (BKCa opener), or 2 μM paxilline (BKCa blocker), starting 25 min before metabolic inhibition. Cell injury was detected by Trypan blue exclusion and lactate dehydrogenase (LDH) release. Chronic hypoxia doubled the number of rod-shaped LVM and SEPM surviving the MI/R insult and reduced LDH release. While NS-1619 protected cells from normoxic rats, it had no additive salutary effect in the hypoxic group. Paxilline attenuated the improved resistance of cells from hypoxic animals without affecting normoxic controls; it also abolished the protective effect of NS-1619 on LDH release in the normoxic group. While chronic hypoxia did not affect protein abundance of the BKCa channel regulatory β1-subunit, it markedly decreased its glycosylation level. It is concluded that ventricular myocytes isolated from chronically hypoxic rats retain the improved resistance against injury caused by MI/R. Activation of the mitochondrial BKCa channel likely contributes to this protective effect.