Effects of season (summer & winter) on electrical characteristics of skeletal muscle membranes of the spiny-tailed lizard, Uromastix hardwickii.

This study deals with the observation of changes with temperature variations of the seasons in the muscular electrical excitability in the reptile Uromastix hardwickii. Freshly captured adult animals of both the sexes were used in all the experiments, and the gastrocnemius (skeletal) muscles were dissected out. The muscle samples were digested with digestive fluid (pepsin & Hcl), stirred, settled and supernatant was removed, till whitish fluid having clear cells obtained for patch clamp recording of ionic currents and potentials. Resting membrane potentials and action potentials of reptilian cell membranes were measured in whole cell current mode. The glass microelectrodes, with a tip diameter 2-3 microm and tip resistance 5-6 MW (when filled with intracellular solution) were used in these experiments. The present study was carried out to investigate the electrical characteristics of the skeletal muscles of this species of Uromastix, which are not studied earlier. The average mean values of resting membrane potential, action potential and its durations showed no significant changes with the change in the season, but other components of action potential including threshold potential, after-potential and its duration were found to be increased significantly (P < 0.05) in summer as compared to winter. Temperature dependency of these parameters with seasonal variation, are studied for the first time in the gastrocnemius (skeletal) muscles of Uromastix hardwickii. Hence seasonal changes in the components of action potential are invariably associated with changes in environmental temperature, and may be responsible for changes in the activities and homeostasis of these animals; and possibly indicating underlying mechanism of hibernation.

Nigella sativa extract as a potent antioxidant for petrochemical-induced oxidative stress.

Various beneficial properties has been attributed to Nigella sativa, including its antioxidant potential. Previously, it was reported that supercritical fluid extraction (SFE) could be used to obtain N. sativa extract rich in antioxidants. In the present study, N. sativa extracts prepared using the previously optimized SFE as well as the traditional Soxhlet extraction approaches were analyzed for various known antioxidants. N. sativa extracts were found to prevent protein carbonyl formation as well as depletion of intracellular glutathione (GSH) in fibroblasts exposed to toluene. Furthermore, partially purified SFE and Soxhlet fractions could prevent loss of hepatic GSH in toluene-induced oxidative stressed Wistar rats as well as in L929 fibroblasts. The results showed that SFE-produced N. sativa extract is richer in antioxidants than the Soxhlet approach. It was also shown using preparative silica gel and reverse phase chromatography that different fractions of SFE-extracted or Soxhlet-extracted N. sativa had different levels of protective effects with regards to GSH depletion in vivo as well as in cell culture. Although fractions rich in thymoquinone were found to be most potent in terms of antioxidant capacity, the data indicates that the protective effects of N. sativa may not only be due to thymoquinone, but perhaps other antioxidants.

Investigating GABA and its function in platelets as compared to neurons.

We have recently suggested that platelets could be used as a model for neuronal receptors. In this paper we have investigated gamma-aminobutyric acid (GABA) metabolism and GABA receptors in platelets and in cultured neurons to see whether platelets' GABA mimics neuronal GABA receptor activities. We used the ELISA technique for detecting the GABA concentration in platelet rich plasma and cultured neurons. The functional effects of GABA and its receptor ligands on platelets were determined using an aggregometer. We found that the GABA concentration is 30% lower in platelets than in neurons and in both preparations GABA was metabolized by GABA transaminase (GABA-T). GABA potentiated calcium dependent platelet aggregation with a higher value in washed platelets suspension (WPS) then in platelet rich plasma (PRP). This effect was inhibited by benzodiazepines, calcium channel blockers and the selective phosphoinositide 3-kinase antagonist Wortmannin. GABA neurotransmission is involved in most aspects of normal brain function and can be perturbed in many neuropathologic conditions. We concluded that platelets could be further developed to be used as a peripheral model to study neuronal GABAergic function and its abnormality in diseases such as epilepsy and schizophrenia. Furthermore our results indicated that PI3-kinase is involved in calcium dependent GABA induced platelet aggregation as this synergistic effect is inhibited by Wortmannin in dose dependent manner.

Patch Clamp Study of Serotonin-Gated Currents via 5-HT Type 3 Receptors by Using a Novel Approach SHAM for Receptor Channel Scanning.

We studied 5-hydroxy tryptamine type 3 (5-HT(3)) receptors transfected in tsA-201 cell line to examine serotonin-induced whole cell currents. Using the site-directed mutagenesis technique, we individually mutated each residue in the membrane-spanning M2 segment to histidine. A high proportion of tsA-201 cells cotransfected with the cDNAs of 5-HT(3)R and CD8 produced large amplitude responses (0.5–7.0 nA) to serotonin. The dose-response curve of wild-type (WT) receptor ranging from 0.5 to 500 $\mu$ mole increases its K(d) values, and I_\mathrm{max} of 5-HT(3)R falls at low external pH as if protonation of an acid group is enough to block the channel. Lysine at position 281, a basic residue, is more susceptible to acidification-induced blockade of the 5-HT(3)R channel. Dose-response curves of K281S (replacing lysine at the 281 position with serine) at different pH are not significantly modulated, and histidine substitutions at the three consecutive positions 293, 294, and 296 eliminate the pH block of the channel.