The phospholipid profiles of the myocardium (from 10- and 18-day old chick embryos and 13-day old chick) and their in vitro response to the endogenous lipolytic enzymes (mainly of the phospholipase group) at pH 7.4 and 38 degrees C for 60 min were analyzed by TLC technology and densitometry. Cardiolipin (CL) was shown to be one of the major phospholipids of the chick embryo myocardium and its concentration increased as the chick embryo advanced in development. Monolysocardiolipin (MLCL) was produced subsequent to in vitro incubation of whole tissue homogenates in all myocardia studied as well as a concurrent reduction in CL. This deacylation of CL increased in magnitude as the chick embryo advanced in development indicating its age relatedness. The level of phosphatidyl ethanolamine (PE) plasmalogen was also high in all myocardia studied. Lyso alkenyl PE (LPE) was produced subsequent to in vitro incubation and its level increased as the chick embryo advanced in development, indicating PLA(2) action on the sn-2 fatty acid of PE. Phosphatidyl choline (PC) plasmalogen was also present in the chick embryo myocardium and its level increased gradually as the chick embryo advanced in development. In contrast, yolk-sac membrane contains very minute amounts of CL and PE. No PC was detected and no LPE was formed following in vitro incubation. The yolk of the unfertilized chicken egg has no CL and has very minute amounts of PE, no PC and no lysophospholipids were detected following in vitro incubation in all samples analyzed.
Several detailed reviews on cellular phospholipase A2 (cPLA2) have been published, however the role of cPLA2 in cell function remains unclear. Continued substantive efforts are required to elucidate a broader understanding of the in vivo functionality for all endogenous phospholipases and an explanation for the need for such diverse phospholipids in various biological membranes, which are not yet at hand.
Recently, we have reported on the preferential deacylation of cardiolipin (CL) of various mammalian myocardia by an endogenous phospholipase (PLA1 and/or PLA2), following in vitro incubation at pH 7.4 and 38°C for 60 minutes of whole tissue homogenate (as source of phospholipids and phospholipases) producing monolysocardiolipin (MLCL) and concurrent reduction of CL. In contrast whole tissue homogenate of rabbit spleen treated similarly selectively deacylated ethanolamine plasmalogen (PE) producing lyso alkenyl PE.
In the present study, whole tissue homogenate of bullfrog cardiac muscle and thigh skeletal muscle, treated similarly revealed the following data: Bullfrog cardiac muscle slightly deacylated CL producing MLCL, Thigh skeletal muscle shows very minute amount of CL and no deacylation products following in vitro incubation, PE plasmalogen is the only alkenyl species of both tissues, Thigh muscle has very minute amount of Sphingomyelin.
These data raised some questions pertaining to the Lipolytic capabilities of diverse tissues from different species of animals and will be discussed in details.
The phosphoglycerides profile of guinea pig kidney, fetal, young adult, and aged, and their in vitro response to the endogenous lipolytic enzymes, mainly in the phospholipase group were determined by TLC technology in conjunction with densitometric measurement. Changes in phosphoglycerides profile subsequent to in vitro incubation of these tissues at pH 7.4, and 38 degrees C for 45 min and prior to phospholipid extraction has provided evidence relating to their respective lipolytic enzymes capabilities and age. These changes are mainly related to endogenous cardiolipin (CL), alkenyl phospholipids (phosphatidyl ethanolamine and phosphatidyl choline) and their endogenous deacylation to their respective lyso derivatives monolysocardiolipin (MLCL), lyso alkenyl phosphatidyl ethanolamine (LPE), and lyso alkenyl phosphatidyl choline (LPC) by endogenous phospholipases. The hydrolysis of the plasmalogen confirms the action of endogenous PLA(2) on sn-2 fatty acids of these compounds.
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