P. G. Kostyuk

Two ion-selecting filters in the calcium channel of the somatic membrane of mollusc neurons

SummaryThe slow inward current carried by Na+ through potential-dependent calcium channels in conditions when divalent cations were removed from the extracellular solution by EDTA has been investigated on isolated internally perfused neurons of the snailHelix pomatia. The calcium channels also acquire the capability to pass monovalent cations if other calcium-binding substances are added to the extracellular solution. Based on these facts the conclusion is made that the immediate reason for the modification of the channel selectivity is the absence of divalent cations in the extracellular medium. All potential-dependent characteristics of the modified calcium channel are shifted by 60 to 70 mV in the hyperpolarizing direction compared with those of the original calcium channel. The series of relative permeabilities for modified calcium channels towards monovalent cations (

Three types of calcium channels in the membrane of mouse sensory neurons

P_{Na^ + } :P_{Li^ + } :P_{N_2 H_5 ^ + } :P_{NH_3 OH^ + }

Activation of P2-purino-,α1-adreno and H1-histamine receptors triggers cytoplasmic calcium signalling in cerebellar purkinje neurons

=1.0∶0.8∶0.55∶0.21) is close to that of common “fast” sodium channels (

Diabetes-induced abnormalities in ER calcium mobilization in primary and secondary nociceptive neurons

P_{Na^ + } :P_{Li^ + } :P_{N_2 H_5 ^ + } :P_{NH_3 OH^ + }

ATP induces Ca2+ release from IP3-sensitive Ca2+ stores exclusively in large DRG neurones.

=1.0∶1.04∶0.44∶0.21). The induced sodium current decreases immediately when the concentration of divalent cations in the extracellular solution is elevated. This decrease is not potential dependent and can be approximated by Langmuirs isotherm with dissociation constants pKCa∶pKSr∶pKBa∶pKMg=6.6∶5.5∶4.8∶4.2. The conclusion is drawn that the calcium channels in the somatic membrane have two ion-selecting filters with different functions —an external one consisting, probably, of several carboxylic groups which bind divalent cations in a highly specific manner and determine the impermeability of the channel to monovalent cations in physiological conditions, and the channel ion-selecting filter including a single carboxylic group normally determining the channel selectivity for different divalent cations.

Gradual caffeine-induced Ca2+ release in mouse dorsal root ganglion neurons is controlled by cytoplasmic and luminal Ca2+.

Free intracellular calcium concentration ([Ca2+]in) was recorded at 22 degrees C by means of Indo-1 or Fura-2 single-cell microfluorometry in cultured dorsal root ganglion neurons obtained from neonatal rats. The resting [Ca2+]in in dorsal root ganglion neurons was 73 +/- 21 nM (mean +/- S.D., n = 94). Fast application of 20 mM caffeine evoked [Ca2+]in transient which reached a peak of 269 +/- 64 nM within 5.9 +/- 1.1 s. After reaching the peak the [Ca2+]in level started to decline in the presence of caffeine and for 87.2 +/- 10.6 s cytoplasmic calcium returned to an initial resting value. In 40% of neurons tested [Ca2+]in decreased to subresting levels following the washout of caffeine (the so-called post-caffeine undershoot). On average, the undershoot level was 19 +/- 2.5 nM below the resting [Ca2+]in value. Prolonged exposure of caffeine depleted the caffeine-sensitive stores of releasable Ca2+; the degree of this depletion depended on caffeine concentration. The depletion of the caffeine-sensitive internal stores to some extent was linked to calcium extrusion via La(3+)-sensitive plasmalemmal Ca(2+)-ATPases. The stores could be partially refilled by the uptake of cytoplasmic Ca2+, but the complete recovery of releasable Ca2+ content of the caffeine-sensitive pools required the additional calcium entry via voltage-operated calcium channels. Caffeine-evoked [Ca2+]in transients were effectively blocked by 10 microM ryanodine, 5 mM procaine, 10 microM dantrolene or 0.5 mM Ba2+, thus sharing the basic properties of the Ca(2+)-induced-Ca2+ release from endoplasmic reticulum. Pharmacological manipulation with caffeine-sensitive stores interfered with the depolarization-induced [Ca2+]in transients. In the presence of low caffeine concentration (0.5-1 mM) in the extracellular solution the rate of rise of the depolarization-triggered [Ca2+]in transients significantly increased (by a factor 2.15 +/- 0.29) suggesting the occurrence of Ca(2+)-induced Ca2+ release. When the caffeine-sensitive stores were emptied by prolonged application of caffeine, the amplitude and the rate of rise of the depolarization-induced [Ca2+]in transients were decreased. These facts suggest the involvement of internal caffeine-sensitive calcium stores in the generation of calcium signal in sensory neurons.