TLC characterization of liposomes containing D-myo-inositol derivatives

Inositol trisphosphate and cyclic adenosine diphosphate-ribose increase quantal transmitter release at frog motor nerve terminals: possible involvement of smooth endoplasmic reticulum

The release of chemical transmitter from nerve terminals is critically dependent on a transient increase in intracellular Ca2+. The increase in Ca2+ may be due to influx of Ca2+ from the extracellular fluid or release of Ca2+ from intracellular stores such as mitochondria. Whether Ca2+ utilized in transmitter release is liberated from organelles other than mitochondria is uncertain. Smooth endoplasmic reticulum is known to release Ca2+, e.g., on activation by inositol trisphosphate or cyclic adenosine diphosphate-ribose, so the possibility exists that Ca2+ from this source may be involved in the events leading to exocytosis. We examined this hypothesis by testing whether inositol trisphosphate and cyclic adenosine diphosphate-ribose modified transmitter release. We used liposomes to deliver these agents into the cytoplasmic compartment and binomial analysis to determine their effects on the quantal components of transmitter release. Administration of inositol trisphosphate (10(-4)M) caused a rapid, 25% increase in the number of quanta released. This was due to an increase in the number of functional release sites, as the other quantal parameters were unaffected. The effect was reversed with 40 min of wash. Virtually identical results were obtained with cyclic adenosine diphosphate-ribose (10(-4)M). Inositol trisphosphate caused a 10% increase in quantal size, whereas cyclic adenosine diphosphate-ribose had no effect. The results suggest that quantal transmitter release can be increased by Ca2+ released from smooth endoplasmic reticulum upon stimulation by inositol trisphosphate or cyclic adenosine diphosphate-ribose. This may involve priming of synaptic vesicles at the release sites or mobilization of vesicles to the active zone. Inositol trisphosphate may have an additional action to increase the content of transmitter within the vesicles. These findings raise the possibility of a role of endogenous inositol phosphate and smooth endoplasmic reticulum in the regulation of cytoplasmic Ca2+ and transmitter release.

Extracellular and intracellular arachidonic acid-induced contractions in rat aorta

Arachidonic acid induced contractions of de-endothelized rat aortic rings. A more potent effect was obtained after intracellular administration of arachidonic acid using liposomes. Contractions induced by extracellular arachidonic acid were inhibited similarly to phenylephrine-induced contractions by the L-type Ca2+ channel blocker, methoxyverapamil (D600), and the calmodulin inhibitor, calmidazolium. In contrast, contractions induced by arachidonic acid-filled liposomes were not affected by these compounds. Indomethacin did not affect the contractions induced by either extra- or intracellular arachidonic acid, whereas nordihydroguaiaretic acid relaxed contractions induced by extracellular arachidonic acid but not those induced by arachidonic acid-filled liposomes. Apart from a relaxing effect on contractions induced by extracellular arachidonic acid or by phenylephrine, protein kinase C inhibition with 1-(5-isoquinolinesulphonyl-2-methylpiperazine (H7)) had an even more prominent relaxing effect on contractions induced by arachidonic acid-filled liposomes. Therefore, arachidonic acid exerts a contractile effect on rat aorta, and this effect is regulated differently depending on the site of application.

TLC characterization of liposomes containing angiotensinogen, angiotensine I, angiotensine II and saralazin

Recent studies have described intracellular binding sites for angiotensine II. In vascular smooth muscle it was found that intracellular injection of angiotensin II increases the Ca2+ level. An alternative method for intracellular delivery of drugs is represented by using liposomes. Thus, the aim of this study was to characterize liposomes filled with angiotensinogen, angiotensine I (Ang I), angiotensine II (Ang II), and saralasin by a TLC method and examine the physiological effects of these on rat vascular smooth muscle. Ang II (for all concentrations tested in the aqueous phase) and Ang I (for concentrations less than 10(-4)M) did not affect the thin-layer chromatography migration of this type of vesicle, suggesting that dose-dependent effects on physio-pharmacological experiments could be studied. On the other hand, this type of experiment could not be performed for salarasin- or angiotensinogen-filled liposomes. Administration of liposomes containing Ang II (10(-6)M), Ang I (10(-6)M), angiotensinogen (10(-6)M) and saralasine (10(-6)M) caused the contraction to isolated rat aorta smooth muscle, suggesting the presence of active intracellular binding sites.

TLC characterization of small unilamellar liposomes containing D-myo-inositol derivatives

The thin-layer chromatographic (TLC) behaviour of small unilamellar liposomes containing inositol phosphates (IPs) was studied. The vesicles contained different concentrations of D-myo-inositol 1,4,5-triphosphate (IP3), D-myo-inositol 1,2,6-triphosphate (alpha-trinositol, PP 56, a novel Perstorp Pharma derivative), D-myo-inositol 1,3,4,5-tetraphosphate (IP4), D-myo-inositol 1,3,4,5,6-pentakisphosphate (IP5) and D-myo-inositol 1,2,3,4,5,6-hexakisphosphate (IP6). Migration of all liposome batches was compared to that of control liposomes (multilamellar and small unilamellar, both containing only triple-distilled water), and to that of free phosphatidylcholine (PC). The same amount of lipid was used in all situations. Thin-layer chromatography was performed with silica gel as adsorbent. The developing solvent was an n-buthanol:ethanol:water mixture in a 4:3:3 volume ratio. At doses higher than 10(-2) M liposomes containing alpha-trinositol and IP6 had a different migration than PC, MLV or SUV as well as all batches of liposomes. Physiological studies (using as model endothelized rat aorta rings) proved that in this situation they had no effects.