Inactivation of cGMP-dependent conductance of rod outer segment plasma membrane induced by cGMP

Time-dependent metabolomics study of cerebral ischemia-reperfusion and its treatment: focus on the combination of traditional Chinese medicine and Western medicine

Cerebral ischemia is a common cerebrovascular disease with high mortality, and thrombolysis can cause more severe reperfusion injury. In clinical practice, Ginkgo biloba dispersible tablets combined with nimodipine have been widely used to reduce cerebral ischemia-reperfusion injury, but the mechanism has not been clearly elucidated. To explore this relationship, the change in metabolism between a sham operation group, a model group and an administration group was analyzed for the period after cerebral ischemia. Biochemical assays were used to assess injury extent and the therapeutic effects of different dosing regimens. A metabolomics method based on ultrahigh-performance liquid chromatography-quadrupole time-of-flight mass spectrometry was developed to screen biomarkers in plasma of rats and analyze abnormal metabolic pathways. Using statistical analysis, corticosterone, glutamine, oleic acid, isoleucine, phenylalanine and sphingomyelin (d18:1/16:0) were screened as diagnostic biomarkers. The metabolic pathways perturbed by cerebral ischemia-reperfusion involved phenylalanine, tyrosine and tryptophan biosynthesis, phenylalanine metabolism, alpha-linolenic acid metabolism, retinol metabolism, alanine, aspartate and glutamate metabolism, and glycerophospholipid metabolism. Analysis of the adjustment of biomarkers at different time points showed that the best time to evaluate the efficacy of combined administration is about 6 h after administration. Both pathological characteristics and metabolomics confirmed the better effect of the combined group than the individual groups. In this study, a non-targeted metabolomics method was developed to explore the mechanism of action of the combination of traditional Chinese and Western medicine in cerebral ischemia-reperfusion treatment, providing a theoretical basis for disease prognosis and treatment options. Graphical abstract.

Expression of subunits for the cAMP-sensitive 'olfactory' cyclic nucleotide-gated ion channel in the cochlea: implications for signal transduction

Cyclic nucleotide-gated (CNG) ion channels have been implicated as functioning in sensory transduction and in second-messenger modulation of synaptic neurotransmitter release. The olfactory, cAMP-sensitive CNG ion channel in vivo is considered to comprise the pore-forming CNG2 subunit together with CNG5 and CNG4.3 modulatory subunits. The expression of these 'olfactory' CNG subunit transcripts in microdissected subfractions of the rat cochlea and hair cell libraries has been investigated with RT-PCR. Unmodified transcripts of CNG2 were detected in the organ of Corti, lateral wall and spiral ganglion subfractions. CNG5 message was found in both the sensory organ of Corti and the non-sensory lateral wall subfractions but not in the spiral ganglion subfraction. The CNG5 sequence obtained for the organ of Corti fraction encompassed 78% of the olfactory CNG5 cDNA sequence. CNG5 message has also been detected in an inner hair cell cDNA library. In the lateral wall, unmodified CNG5 sequence was observed as well as truncated versions of CNG5 transcripts, one of which was also found in the rat brain. The truncated versions were characterized by deletions that resulted in a shift in reading frame and the premature appearance of a stop codon. The 'olfactory' CNG4.3 cDNA was amplified from all three subfractions. Within the cochlea, CNG2 immunoreactivity was selectively distributed in a pattern similar to that of adenylyl cyclase type I. Immunoreactivity to CNG2 has been localized to stereocilia of inner hair cells. CNG5 immunoreactivity was associated with stereocilia and lateral plasma membranes of outer hair cells. We conclude that transcripts necessary for a functional cAMP-sensitive CNG ion channel are present in the cochlea resulting from combinations of CNG2 with CNG5 and CNG4.3. Further, the localization of CNG2 and CNG5 immunoreactivity to hair cell stereocilia suggests a role for cAMP-sensitive CNG channels in hair cell signal transduction.

Cyclic nucleotide-activated channels in carp olfactory receptor cells

When applied from the cytoplasmic side, cyclic 3',5'-adenosine and guanosine monophosphates reversibly increased the ion permeability of inside-out patches of carp olfactory neuron plasma membrane. The cAMP (cGMP)-induced permeability via cAMP (cGMP) concentration was fitted by Hill's equation with the exponents of 1.07 +/- 0.15 (1.12 +/- 0.05) and EC50 = 1.3 +/- 0.6 microM (0.9 +/- 0.3 microM). Substitution of NaCl in the bathing solution by chlorides of other alkali metals resulted in a slight shift of reversal potential of the cyclic nucleotide-dependent (CN) current, which indicates a weak selectivity of the channels. Permeability coefficients calculated by Goldman-Hodgkin-Katz's equation corresponded to the following relation: PNa/PK/PLi/PRb/PCs = 1:0.98:0.94:0.70:0.61. Ca2+ and Mg2+ in physiological concentrations blocked the channels activated by cyclic nucleotides (CN-channels). In the absence of divalent cations the conductance of single CN-channels was equal to 51 +/- 9 pS in 100 mM NaCl solution. Channel density did not exceed 1 micron-2. The maximal open state probability of the channel (Po) tended towards 1.0 at a high concentration of cAMP or cGMP. Dichlorobenzamil decreased Po without changing the single CN-channel' conductance. CN-channels exhibited burst activity. Mean open and closed times as well as the burst duration depended on agonist concentration. A kinetic model with four states (an inactivated, a closed and two open ones) is suggested to explain the regularities of CN-channel gating and dose-response relations.

Interactions between divalent cations and the gating machinery of cyclic GMP-activated channels in salamander retinal rods

The effects of divalent cations on the gating of the cGMP-activated channel, and the effects of gating on the movement of divalent cations in and out of the channel's pore were studied by recording macroscopic currents in excised membrane patches from salamander retinal rods. The fractional block of cGMP-activated Na+ currents by internal and external Mg2+ as well as internal Ca2+ was nearly independent of cGMP concentration. This indicates that Mg2+ and Ca2+ bind with similar affinity to open and closed states of the channel. In contrast, the efficiency of block by internal Cd2+ or Zn2+ increased in proportion to the fraction of open channels, indicating that these ions preferentially occupy open channels. The kinetics of block by internal Ni2+, which competes with Mg2+ but blocks more slowly, were found to be unaffected by the fraction of channels open. External Ni2+, however, blocked and unblocked much more rapidly when channels were mostly open. This suggests that within the pore a gate is located between the binding site(s) for ions and the extracellular mouth of the channel. Micromolar concentrations of the transition metal divalent cations Ni2+, Cd2+, Zn2+, and Mn2+ applied to the cytoplasmic surface of a patch potentiated the response to subsaturating concentrations of cGMP without affecting the maximum current induced by saturating cGMP. The concentration of cGMP that opened half the channels was often lowered by a factor of three or more. Potentiation persisted after the experimental chamber was washed with divalent-free solution and fresh cGMP was applied, indicating that it does not result from an interaction between divalent cations and cGMP in solution; 1 mM EDTA or isotonic MgCl2 reversed potentiation. Voltage-jump experiments suggest that potentiation results from an increase in the rate of cGMP binding. Lowering the ionic strength of the bathing solution enhanced potentiation, suggesting that it involves electrostatic interactions. The strong electrostatic effect on cGMP binding and absence of effect on ion permeation through open channels implies that the cGMP binding sites on the channel are well separated from the permeation pathway.

A cyclic-AMP-gated conductance in cochlear hair cells

The patch clamp technique was used to record cAMP-dependent currents of the guinea pig cochlear hair cell plasma membrane. Data obtained indicate that the channels passing this current are moderately selective for monovalent cations and are effectively blocked by L-cis-diltiazem and reversibly blocked by 1 mM Mg2+ or Ca2+. The single-channel unit conductance estimated in the absence of divalent cations is about 16 pS. The results demonstrate that cyclic nucleotide-dependent channels of cochlear hair cells are virtually identical to the photoreceptor and olfactory ones.

Cyclic nucleotide-activated channels in the frog olfactory receptor plasma membrane

Patch clamp technique was used to record cyclic nucleotide-dependent current of the frog olfactory receptor cell plasma membrane. Data obtained indicate that the channels passing this current are permeable to Ca2+ or Mg2+ and moderately selective for monovalent cations according to the sequence Li+, Na+, K+ greater than Rb+ greater than Cs+ and are effectively blocked by 1-cis-diltiazem and 3',4'-dichlorobenzamil. The conductance of single cyclic nucleotide-gated channels in solutions with low Ca2+ and Mg2+ content is about 19 pS. The results demonstrate that cyclic nucleotide-activated channels of olfactory receptor cells are virtually identical to photoreceptor ones.