Both voltage-activated potassium channels and the concentration of free intracellular calcium have been implicated in the activation of T lymphocytes. Using the patch-clamp technique, we now show an unexpected relationship between the level of intracellular calcium [Ca]i in human lymphocytes and the amplitude of a voltage-dependent current: the elevation of [Ca]i decreases the potassium conductance. This is in contrast to other systems where [Ca]i activates K+ channels. Our results suggest that the level of intracellular calcium regulates the effective number of K+ channels capable of being activated.

1 The membrane response to applied histamine of cultured endothelial cells from human umbilical vein was studied by use of whole cell and single channel patch clamp techniques. A value of -27 + 1.4 mV was found for the resting potential under whole cell current clamp. No voltage-gated currents were seen at either the macroscopic or single channel levels. 2 At holding potentials of -20 to -40 mV, histamine evoked slow rising, long lasting whole cell inward currents. The inward current was associated with depolarization and decreased input resistance. The calcium ionophore A23187 provoked similar whole cell inward currents. 3 Single channel currents were observed in cell-attached and inside-out patches for both histamine and A23187. The single channel conductance was about 20 pS with a mean open time of 5 ms and a reversal potential of OmV in symmetrical potassium solutions. Internal sodium blocked outward going currents. 4 For cell-attached patches, histamine-dependent channel activity required external calcium and was also seen when histamine was present in the bath but not the pipette. Recording from insideout patches revealed that decreases in 'internal' calcium resulted in the disappearance of channel activity. 5 The histamine-dependent inward current appears to involve calcium-dependent activation of cationic channels.

1. The effects of anoxia on inhibitory synaptic transmission were studied in hippocampal slices of 3- to 4-wk-old rats. CA1 pyramidal cells were examined by whole-cell patch-clamp recording. Synaptic currents were evoked by "distant" (> 0.5 mm) or "close" (< 0.5 mm) electrical stimulation in the stratum radiatum. 2. The excitatory postsynaptic currents (EPSCs) and inhibitory postsynaptic currents (IPSCs) evoked by distant stimulation were completely suppressed by brief anoxia (95% N2-5% CO2 for 4-6 min) and recovered upon reoxygenation. IPSCs were more sensitive to anoxia than EPSCs. EPSCs and IPSCs evoked by distant stimulation were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 20 microM) and D-2-amino-5-phosphonopentanoate (APV; 50 microM). This indicates that IPSCs were mediated via a polysynaptic pathway that involves glutamate receptors. 3. Synaptic currents evoked by close stimulation were only partly inhibited by anoxia. The bicuculline-sensitive gamma-aminobutyric acid-A (GABAA) receptor-mediated synaptic currents were particularly resistant to anoxia, suggesting that the GABAergic input to pyramidal neurons is not inhibited by anoxia. 4. At close stimulation in the stratum radiatum, monosynaptic IPSCs could be evoked in the presence of CNQX (20 microM) and APV (50 microM). The monosynaptic IPSCs had early bicuculline (15 microM) and late CGP 35348 (100 microM)-sensitive components confirming an involvement of GABAA and GABAB receptors (IPSCA and IPSCB components), respectively. 5. The monosynaptic IPSCA component evoked by close stimulation was not changed significantly during and after brief anoxia. Responses to pressure application of isoguvacine (GABAA agonist) were also not affected by anoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Ca2+-activated K+ ionic currents in the membrane of cultured smooth muscle cells isolated from foetal and adult human aorta were studied using whole cell and single-channel patch-clamp techniques. Whole cell currents in adult smooth muscle cells were 3-8 times larger than in foetal cells of similar sizes. The elementary conductance and ionic selectivity of single Ca2+-activated K+ were identical for both types of cells. Channel openings occurred in burst, the duration of which was 3-5-fold longer in adult than in foetal cells. The voltage dependency of the channel activating mechanism and the dependency of the mean open time on the Ca2+ concentration on the inner side of the membrane were similar for both types of cells. These results suggest that the main reason for the increase in potassium conductance during development is an alteration in the open time of the Ca2+-activated K+ channels.

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