Lipidic characterization of full‐grown amphibian oocytes and their plasma membrane‐enriched fractions

Abstract

The content and composition of neutral lipids and phosphoglycerides from full-grown prophase-arrested Bufo arenarum Hensel oocytes and from their ghost preparations were studied. The ghosts obtained are highly enriched in plasma membrane as suggested by the activity of 5'-nucleotidase, a marker enzyme, and the level of typical membrane components such as sphingomyelin, phosphatidylserine (PS), phosphatidylinositol (PI), and phosphatidic acid. In whole oocytes, triacylglyceride (TAG) comprises about 60% of the total lipids followed by phosphatidylcholine (PC), cholesterol, and phosphatidylethanolamine (PE). TAG and diacylglycerides have a similar unsaturation index. PC and PE account for about 80% of the phosphoglycerides in the whole oocyte and in their plasma membrane-enriched fractions. Arachidonic acid (20:4n-6), 18:0, and 16:0 make up about 80 mol% of the total fatty acids in PI in whole oocytes and ghost fractions. The unsaturation index in PS is higher in intact oocytes than in ghost preparations, probably owing to the significant amount of 20:4n-6 which comprises 23 mol% of the total fatty acids in whole oocytes. The fatty acid profile in phosphatidic acid from whole oocytes is rather different from that in ghosts. Sphingomyelin contains mainly saturated and monounsaturated fatty acids, 24:1 being the principal very long chain unsaturated fatty acid in both oocytes and ghosts.

Involvement of PLA2, COX and LOX inRhinella arenarumoocyte maturation

“…In zebrafish, Lister & Van Der Kraak (2008) showed that follicles expressed enzymes that were involved in AA release, such as phospholipase A 2 (PLA 2 ) and phospholipase C γ1 , or enzymes that can metabolize AA such as COX 1 , COX 2 and prostaglandin synthase-2. In agreement with this finding, it was shown in Rhinella arenarum that P 4 -induced maturation caused significant changes in the amount and composition of phospholipids and neutral lipids in both fully grown ovarian oocytes and plasma membrane-enriched fractions (Caldironi & Alonso, 1996; Mata et al ., 2000; Zelarayán et al ., 1999). These changes may occur due to lipolytic enzymes activation, especially PLA 2 , that release AA.…”

“…In starfish, arachidonic acid (AA) and eicosapentaenoic acid were capable of inducing maturation. In agreement with this finding, it was shown in Rhinella arenarum that P 4 -induced maturation caused significant changes in the amount and composition of phospholipids and neutral lipids in both fully grown ovarian oocytes and plasma membrane-enriched fractions (Caldironi & Alonso, 1996;Mata et al, 2000;Zelarayán et al, 1999). PUFAs appear to be involved in the mechanism by which methyladenine induces oocyte maturation (Meijer et al, 1986).…”

Lipids during Bufo arenarum oogenesis

“…The larger content of SM in stage IV and V oocytes with respect to stage III oocytes could be related to the above-mentioned role of this phospholipid in the maturation process that stage V oocytes may undergo. In full-grown B. arenarum and X. laevis oocytes, PC has the same abundant acyl groups (Alonso et al, 1987;Caldironi & Alonso, 1996). The PC/SM and total phospholipids/SM ratios in stage III oocytes are higher than the ratios found in stage IV and V oocytes.…”

“…Results are shown as mean values ± SD (mol%) from three independent samples for SFA (saturated fatty acids), MUFA (monounsaturated fatty acids) and PUFA (polyunsaturated fatty acids). Caldironi & Alonso (1996) reported that TAG from full-grown oocytes has the same main acyl groups. sise eicosanoids as prostaglandins, thromboxanes and leukotrienes and various hydroxyeicosatetraenoic acids and epoxyeicosatrienoic acids.…”

Effects of temperature on human L-type cardiac Ca 2+ channels expressed in Xenopus oocytes

“…Thus, our data obtained using the α 1C-∆1633 subunit may not represent the expression of the channel moiety alone, and subunit interactions may still arise. That the expression system itself may affect Q 10 is also a possibility; however, the membrane lipid composition of defolliculated amphibian oocytes [4] is not greatly different from that of the cardiac sarcolemma (see [35]). Furthermore, as the channel voltage sensors reside on the α 1 subunit [14] and as V a and K a are affected by temperature, other critical domains may be involved in the activation process.…”