Hydrogen sulfide (H2S) is a novel gasotransmitter that inhibits L-type calcium currents (I Ca, L). However, the underlying molecular mechanisms are unclear. In particular, the targeting site in the L-type calcium channel where H2S functions remains unknown. The study was designed to investigate if the sulfhydryl group could be the possible targeting site in the L-type calcium channel in rat cardiomyocytes. Cardiac function was measured in isolated perfused rat hearts. The L-type calcium currents were recorded by using a whole cell voltage clamp technique on the isolated cardiomyocytes. The L-type calcium channel containing free sulfhydryl groups in H9C2 cells were measured by using Western blot. The results showed that sodium hydrosulfide (NaHS, an H2S donor) produced a negative inotropic effect on cardiac function, which could be partly inhibited by the oxidant sulfhydryl modifier diamide (DM). H2S donor inhibited the peak amplitude of I Ca, L in a concentration-dependent manner. However, dithiothreitol (DTT), a reducing sulfhydryl modifier markedly reversed the H2S donor-induced inhibition of I Ca, L in cardiomyocytes. In contrast, in the presence of DM, H2S donor could not alter cardiac function and L type calcium currents. After the isolated rat heart or the cardiomyocytes were treated with DTT, NaHS could markedly alter cardiac function and L-type calcium currents in cardiomyocytes. Furthermore, NaHS could decrease the functional free sulfhydryl group in the L-type Ca2+ channel, which could be reversed by thiol reductant, either DTT or reduced glutathione. Therefore, our results suggest that H2S might inhibit L-type calcium currents depending on the sulfhydryl group in rat cardiomyocytes.

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Transient receptor potential cation channel 6 (TRPC6) is one of the key molecules for filtration barrier function of podocytes. Over-expression of TRPC6 in podocytes is frequently found in acquired or inherited proteinuric kidney diseases, and animal model over-expression of TRPC6 may lead to proteinuria. To investigate the impact of TRPC6 over-expression in podocytes on its function and its relation to proteinuria in kidney diseases, we over-expressed TRPC6 in mouse podocytes by transient transfection of TRPC6 cDNA plasmid, and observed their changes in foot processes, intracellular F-actin distribution, nephrin and synaptopodin expression, electrophysiology, RhoA activity and intracellular Ca(2+). In podocytes over-expressing TRPC6, cell processes were reduced remarkably in association with the derangement of cytoskeleton demonstrated by the abnormal distribution of intracellular F-actin. These cells also displayed a higher increase of intracellular Ca(2+) ion to the TRPC6 agonist 1-oleoyl-acetyl-sn-glycerol and a higher current in the patch-clamp experiment, down-regulation of nephrin and synaptopodin expression and increase of activated RhoA. These changes could be rescued by the treatment of the cells with U73122 to block TRPC6 channel or BAPTA-AM to chelate intracellular Ca(2+) ion. Additionally, the podocytes over-expressing TRPC6 treated with RhoA inhibitor Y-27632 showed an improvement in F-actin arrangement in the cells and increase of nephrin and synaptopodin expression. From these results, we therefore propose that over-expression of TRPC6 in podocytes may be one of the fundamental changes relating to the dysfunction of the slit diaphragm and proteinuria. Podocytes over-expressing TRPC6 may lead to higher intracellular Ca(2+) ion concentration in the presence of stimuli. The increase of intracellular Ca(2+) down-regulates the expression of two important molecules, nephrin on slit diaphragm and synaptopodin in cytoskeleton, and stimulates RhoA activity, which in turn causes F-actin derangement and the decrease of foot processes.

Previous studies have shown that configurational prey recognition in common toads is performed by feature-analyzing functional units consisting of assemblies of connected neurons such as retinal (classes R2, R3), tectal [classes T5(1), T5(2), T5(3)], and pretectal (class TH3) cells. In the present paper, effects of textured backgrounds on the response of these neurons to a configurational moving stimulus have been tested quantitatively. (1) In all investigated neurons, neither the overall activation nor the respective stimulus-response relationships were significantly influenced by a stationary black/white-textured background as far as black stimulus objects are concerned. (2) The neuronal activity in response to a moving object (signal) could be inhibited (masked) if a black/white-textured background (noise) was moving simultaneously at the same speed. The strength (I) of this 'surround inhibition' (signal masking by the background) was different in the various classes of neurons, i.e. strongest for T5(2) and weakest for R3: I_T5(2) I_T5(1) I_T5(3) > I_R2 > I_TH3 I_R3. These inhibitory effects were not correlated with the size of the neuronal excitatory receptive field (ERF), since T4 neurons (ERF = 180°) in this context displayed response properties similar to T5(2) neurons (ERF < 30°). (3) It is suggested that the signal (prey)-masking effect of a moving textured background is brought about by pretecto (TH3)-tectal [T5(1), T5(2)] inhibitory connectivity which allows toads: (a) to select prey from nonprey; (b) to discriminate between prey and a textured background, and (c) to determine the origin of moving retinal images caused either by object movement or by self-induced motion.

Overload of intracellular calcium caused by amyloid-beta peptide has been implicated in the pathogenesis of neuronal damage in Alzheimer's disease. Voltage-gated calcium channels (VGCCs) provide one of the major sources of Ca(2+) entry into cells. Here, we investigated whether icariin had effect on the changes of calcium currents induced by Abeta(25-35) in hippocampal pyramidal neurons. Using whole-cell patch-clamp, we showed that Abeta(25-35) enhanced the inward Ba(2+) and Ca(2+) currents. The currents were partially inhibited by Ni(2+) and completely suppressed by Cd(2+), indicating that Abeta(25-35) disrupts intracellular calcium homeostasis via the modulation of both L- and T-type channels. Furthermore, icariin nearly complete suppressed the abnormal inward calcium currents induced by Abeta(25-35) in a dose-dependant manner. Our findings suggest that the potential neuroprotective effect of icariin on Abeta(25-35)-induced neurotoxicity via the balance intracelluar calcium homeostasis.