Abstract
The catfish,Ictalurus punctatus, is an important model for studying the biochemical mechanisms of taste at the peripheral level. The type, amount and metabolic activity of the lipids within this tissue play important roles in taste transduction by forming the matrix in which the receptors for taste stimuli are imbedded and by acting as precursors to second messengers. The metabolic interconversions that occur among the lipids on the taste organ (barbels) of this animal are reported here. When sodium [32P]phosphate was incubated with minced pieces of epithelium from the taste organ ofI. punctatus, phospholipids became labeled. Maximal incorporation occurred near 20 min for lysophosphatidylcholines (LPC),phosphatidylcholines (PC) and phosphatidylinositols (PI). The phosphatidylethanolamines (PE) and phosphatidylserines (PS) became labeled more slowly. The label in LPC and PC declined from 20 min to 120 min, while that of the other fractions increased or was stable over the 20–120 min time period. Upon addition of 1,2-di-[1′-14C]palmitoyl-sn-glycero-3-phosphocholine to the medium,14C was found within minutes in all of the phospholipids assayed. The amount of label incorporated increased with time, with maximum labeling for all phospholipids occurring at 15 min. However,14C appeared predominantly first (by 5 min) in a neutral lipid fraction (fraction AG, consisting of free fatty acids, mono- and diglycerides, triglycerides and methyl esters), then declined rapidly as the phospholipids gradually incorporated more label. Within minutes of addition of 1-[1′-14C]palmitoyl-sn-glycero-3-phosphocholine (lysophosphatidylcholine) the14C-label was detected in the neutral lipid fraction AG, then in the PC fraction, and later in the other phospholipids. The PC fraction was maximally labeled by 40 min.
Using the appropriate radiolabeled substrates, lysophosphatidylcholine phospholipase A1 and phosphatidylcholine phospholipase D activities were detected in this tissue. Very low activity of a phosphatidylcholine phospholipase A2 was observed. The experiments indicate that there are active and rapid exchange, degradation, synthesis and scavenger pathways of phospholipids in the taste organ of this animal, and suggest that phospholipases A1 and D-type activities are primarily responsible for the rapid breakdown of LPC and PC.
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Abbreviations
- DMSO:
-
dimethyl sulfoxide
- DPM:
-
disintegration per minute
- HPLC:
-
high performance liquid chromatography
- LPC:
-
lysophosphatidylcholine
- LPC-PLA1:
-
lysophosphati-dylcholine-phospholipase A1
- PA:
-
phosphatidic acid
- PC:
-
phosphatidylcholine(s)
- PC-PLD:
-
phosphatidylcholine-phospholipase D
- PE:
-
phosphatidylethanolamine(s)
- PI:
-
phosphatidylinositol(s)
- PS:
-
phosphatidylserine(s)
- TCA:
-
trichloroacetic acid
- and TLC:
-
thinlayer chromatography
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Rabinowitz, J.L., Huque, T., Brand, J.G. et al. Lipid metabolic interrelationships and phospholipase activity in gustatory epithelium ofictalurus punctatus in vitro . Lipids 25, 181–186 (1990). https://doi.org/10.1007/BF02535745
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DOI: https://doi.org/10.1007/BF02535745