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N K Chemeris

Publications and source records attributed to N K Chemeris.

At least 19 recordsLinked to original sources
PubMed1998

Modulation of the activity of Ca(2+)-activated K+ channels by internal Mg2+ in cultured kidney cells vero.

The inside-out mode of the patch-clamp method was used to study the effects of internal Mg2+ on single large-conductance (193+/-7 pS) Ca(2+)-activated K+ channels in cultured kidney cells. In the absence of Ca2+, Mg2+ (1 to 10 mM) did not activate the channels but modified the activating effect of Ca2+ ions: it decreased the Hill coefficient (n), reduced the apparent dissociation constant (K0.5), and modified the channel open and closed times. K0.5 was found to be a voltage-dependent parameter. In the absence of Mg2+, it averaged 600 microM at -20 mV and 27 microM at +30 mV (22 degrees C, pH 6.8). Mg2+ at saturating concentrations (5 to 10 mM) decreased K0.5 to 50 microM at -20 mV and to 15 microM at +30 mV. Irrespective of the membrane potential, K0.5 tended to its limit value of about 12.6 microM. Thus, the effects of membrane depolarization and Mg2+ exhibited a non-additive, competitive relationship. Mg2+ perturbed the exponential shape of the voltage dependences of K0.5. The Hill coefficient characterizing the interaction of Ca2+ ions with the channels was found to be voltage-dependent. In the absence of Mg2+, it increased rather sharply from approx. 2 to 3.5 when the membrane potential was raised from -10 to 0 mV. Mg2+ increased n in a dose-dependent manner; however, about a twofold increase of n occurred within a narrow concentration range (2 to 3 mM). The action of Mg2+ on n was, apparently, voltage-independent, and the effects of Mg2+ and voltage on n were seemingly additive.

Animals↗
PubMed1995

Preliminary microwave irradiation of water solutions changes their channel-modifying activity.

Earlier we have shown that millimetre microwaves (42.25 GHz) of non-thermal power, upon direct admittance into an experiment bath, greatly influence activation characteristics of single Ca(2+)-dependent K+ channels (in particular, the channel open state probability, Po). Here we present new data showing that similar changes in Po arise due to the substitution of a control bath solution for a preliminary microwave irradiated one of the same composition (100 mmol/l KCl with Ca2+ added), with irradiation time being 20-30 min. Therefore, due to the exposure to the field the solution acquires some new properties that are important for the channel activity. The irradiation terminated, the solution retains a new state for at least 10-20 min (solution memory). The data suggest that the effects of the field on the channels are mediated, at least partially, by changes in the solution properties.

Animals↗
PubMed1995

Dual effects of microwaves on single Ca(2+)-activated K+ channels in cultured kidney cells Vero.

Using the patch voltage-clamp method, possible effects of millimetre microwaves (42.25 GHz) on single Ca(2+)-activated K+ channels in cultured kidney cells (Vero) were investigated. It was found that exposure to the field of non-thermal power (about 100 microW/cm2) for 20-30 min greatly modifies both the Hill coefficient and an apparent affinity of the channels for Ca2+(i). The data suggest that the field alters both cooperativity and binding characteristics of the channel activation by internal Ca2+. The effects depend on initial sensitivity of the channels to Ca2+ and the Ca2+ concentration applied.

Animals↗
PubMed1991

[Effect of the non-hydrolyzable guanosine triphosphate analogue on dopamine modulation of the calcium current in a snail neuron].

Voltage-activated calcium current was recorded in isolated neurons of Lymnaea stagnalis under voltage clamp and intracellular dialysis conditions. Calcium current was modulated by non-hydrolyzable guanine nucleotide analogue, guanosine-5'-0-3-thiotriphosphate (GTP gamma S), in a receptor-mediated manner: effect of 100 microM GTP gamma S was recorded at activation of the dopamine receptor. The results obtained permitted suggesting that the effect of dopamine on calcium channels in these neurons is a GTP-dependent one.

Animals↗
PubMed1988

Modulation of calcium current in snail neurones by dopamine: the role of intracellular free calcium.

The inhibition of voltage-gated Ca-current in Limnaea stagnalis (L.) neurones by dopamine cannot be prevented by intracellular administration of the Ca-chelating agent, EGTA. At the same time, substitution of external Ba2+ for Ca2+ substantially weakens the dopamine-induced inhibition. The Ca-ionophore, A23187, also produces an inhibition, but the inhibitory effect of A23187 and of dopamine on Ca-current are non-additive. These findings allow one to suggest that the entry and increase of free Ca concentration presumably in the narrow submembrane space, but not in the bulk of cytoplasm, is important for development of inhibition of neuronal Ca-current by dopamine.

Animals↗
PubMed1985

Neurotransmitter-induced modulation of neuronal Ca current is not mediated by intracellular Ca2+ or cAMP.

Dopamine (1 microM) inhibits the Ca component of action potential and corresponding electroexcitable Ca current (ICa) in isolated snail neurons. Adrenaline and serotonin also reduce ICa. The inhibition is not related to changes in intracellular Ca2+ or cAMP concentrations: internal application of 10 mM ethyleneglycoltetraacetic acid or 10 microM cAMP in the mixture with 1 mM Mg-ATP and 2 mM theophylline does not influence the action of neurotransmitters on ICa.

Action Potentials↗
PubMed1982

Inhibition of acetylcholine responses by intracellular calcium in Lymnaea stagnalis neurones.

1. Acetylcholine (ACh)-induced currents were studied in completely isolated Lymnaea stagnalis neurones using the voltage-clamp technique. 2. The ACh-activated pathways were shown to be selective for Cl- ions. 3. It was shown that membrane depolarization inhibits ACh-induced conductance. This phenomenon was called 'ACh response inactivation'. 4. Inactivation decreases after lowering the extracellular Ca2+ concentration or after blockade by Mn2+ of the electrically excitable Ca2+ channels. 5. In dialysed neurones an increase of the intracellular Ca2+ concentration inhibits the ACh-induced conductance. 6. The conclusion is made that the inactivation of ACh response by depolarization is initiated by Ca2+ entering the neurone through the electrically excitable Ca channels. 7. The onset and the decay of the ACh response inactivation were studied by analysing the relaxations of the ACh-induced current during and after the application of depolarizing pulses. The most conspicuous relaxation is a slow relaxation observed at the end of a long depolarizing pulse, which appears to reflect the return of the system from the inactivated state to the non-inactivated one. 8. The slow relaxations observed during and after a depolarizing pulse appear correlated with variations of the intracellular Ca2+ concentration, and are distinct from faster relaxations observed in the hyperpolarizing range and attributed to the voltage dependence of the channel open-time.

Acetylcholine↗
PubMed1980

Trypsin-induced masking of tetrodotoxin receptor of the sodium channels in mollusc neurons.

At the early stage of trypsin treatment of mollusc neurons tetrodotoxin cannot block the Na+ current. In the course of further exposure of neurones to trypsin, tetrodotoxin-sensitivity is restored completely, so its temporal loss results from shielding rather than destruction of the tetrodotoxin-binding site. Pronase and papain do not affect the tetrodotoxin action on the Na+ current.

Animals↗
PubMed1980

[Blocking action of nickel, cobalt, manganese, and magnesium ions on the inward current through the potassium channel of Limnea stagnalis pond snail neurons].

The dose-inward current relationship for calcium channel blocking ions of Ni, Co, Mn and Mg was studied by means of intracellular dialysis and voltage clamp in isolated neurons from the mollusc Limnea stagnalis. For all the four ions the effect was described by the Langmuir isotherm with KMn = 0.36 +/- 0.05 m,, KNi = KCo = 0.74 +/- 0.07 mM, KMg = 18.2 +/- 5.00 mM. These bivalent cations compete with current-carrying ions for a common binding site in the channel's entrance.

Animals↗