| Popis: |
The activation of two receptors of skeletal muscle and myotube in culture, the nicotinic acetylcholine receptor (nAChR) and the ATP-activated P2-purinergic receptor (P2R) resulted, in both cases, in increased intracellular levels of diacylglycerol (DAG). In the case of the receptor-ion channel macromolecule the intracellular DAG increases were seen after activation of nAChR by a cholinergic ligand and blocked by the nAChR inhibitors α-bungarotoxin or d-tubocurarine; they were dependent on the presence of external Ca2+, which points to the action of a phospholipase A2, present in the membrane and activated directly, probably via a G-protein, by nAChR. In the second case the P2R activates a G-protein-phospholipase C system which results in phosphoinositide turnover and a simultaneous increase in inositol phosphates and DAG, followed by intracellular Ca2+ movement and influx of Ca2+. It is discussed if DAG increases, when occurring close to the sarcolemma, might result in lipoxygenase products moving into the synapse and acting as “retrograde” signals. A preliminary experiment with arachidonic acid and a mouse phrenic nerve-diaphragm preparation was performed and showed no changes in MEPPs, while higher AA concentrations may have decreased the EPPs’ amplitudes. |
