1. The resting membrane potential of freshly purified normodense human eosinophils bathed in and dialysed with quasi-physiological solutions was -63 + 2 mV (n = 100). 2. In voltage-clamp mode with quasi-physiological internal and external solutions, voltage steps from the holding potential of -60 mV to levels positive to +20 mV resulted in development of a quasi-instantaneous outward current and a slowly developing outward current. The instantaneous current was absent when the cells were bathed in and dialysed with K+-free solution.3. The slow outward current persisted following simultaneous replacement of K+, Na+ and most of the Cl-with largely impermeant ions (tetraethylammonium, N-methyl-D-glucamine and methanesulphonate) and was augmented when the cell was dialysed with a solution of increased buffering capacity for protons. The observed reversal potential of the current closely followed the hydrogen equilibrium potential over a wide range of internal-external pH combinations, indicating that the conductance underlying the slow outward current was highly selective for H+ ions. 4. Acidification of the pipette solution (increasing [H+]1) augmented the outward H+ current and shifted its activation range negatively, whilst acidification of the external solution had the opposite effect. The voltage dependence of the current is modulated by the transmembrane pH gradient so that only outward current could be activated. However, when the outward current was activated by a voltage step, rapid acidification of external solution produced an inward H+ current which rapidly deactivated. 5. The proton current was reversibly inhibited in a voltage-dependent manner by extracellular application of Zn2+. The apparent dissociation constants were 8 nm (at +40 mV), 36 nm (at +70 mV) and 200 nm (at +100 mV).6. The proton current was augmented by exposure to 10 ,UM arachidonic acid. This augmentation consisted of a shift of the voltage dependence of activation to more negative potentials and enhancement of maximum conductance (H,max Assessment of the role of the eosinophil in health and disease eosinophils are now incriminated as important effector cells has proved difficult because these cells constitute only a in a number of diverse human diseases. These include the small percentage of the total leucocyte population. This host response to parasite infestation and tumours, the contrasts with the relatively sophisticated understanding reaction to transplanted tissues, and both allergic and nonthat exists for the more abundant neutrophil. Nevertheless, allergic inflammatory reactions of the major organ systems (reviewed by Spry, 1988).* To whom correspondence should be addressed. Receptor-directed stimulation of eosinophils and neutrophils leads to the release of a wide repertoire of chemical mediators. Some of these exist preformed within secretory granules, whilst others, such as eicosanoids and oxidants, are generated de novo when the cell is stimulated. Compared with neutrophils, there is a poor understanding of the events that...

SUMMARYCultured astrocytoma cells were voltage clamped with pipettes where [Ca2+] in the pipette was buffered to 10-7 M with 10 mM 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) and membrane currents recorded. In isotonic solution predominantly K+ currents were evoked by depolarizing or hyperpolarizing commands and 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS; 1 mM) had little effect on inward and outward currents evoked by voltage steps to negative and positive potentials. If the osmolarity of the bathing solution was reduced from 280 to 200 mosmol F', a large current developed, which rectified outwardly and reversed close to the equilibrium potential for chloride ions, ECl. Upon stepping to potentials positive to about +30 mV in hypotonic solution, this outward current inactivated over 2-3 s; this decline was greater with N-methyl-D-glucamine chloride (NMDG-Cl) in the pipette than when KCl or sodium glutamate was present. Holding at various positive potentials inactivated the current, with half-inactivation occurring around +50 mV. The current reactivated over 2-3 s at potentials negative to about +30 mV. The current evoked by hypotonic solution was inhibited by various putative chloride channel blockers with the order of potency DIDS > SITS (4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid) ; NPPB (5-nitro-2-(3-phenylpropylamino)-benzoic acid) > niflumic acid > 9-AC (anthracene 9-carboxylic acid). The currents inhibited by these compounds reversed close to the calculated EC1. It is concluded that hypotonic solution evokes a large anionic current in these cultured astrocytoma cells largely carried by chloride ions. This current is absent in isotonic solution, when currents are carried mainly by potassium ions. It is likely that the current elicited by hypotonic solution is part of the mechanisms regulating astrocyte volume in vivo.

Using whole‐cell patch‐clamp recording techniques, we have examined voltage‐gated ion currents in a cultured human intestinal smooth muscle cell line (HISM). Experiments were performed at room temperature on cells after passages 16 and 17. Two major components of the whole‐cell current were a tetraethylammonium‐sensitive (IC50= 9 mm), iberiotoxin‐resistant, delayed rectifier K+ current and a Na+ current inhibited by tetrodotoxin (IC50= 100 nm). No measurable inward current via voltage‐gated Ca2+ channels could be detected in these cells even with 10 mm Ca2+ or Ba2+ in the external solution. No current attributable to calcium‐activated K+ channels was found and no cationic current in response to muscarinic receptor activation was present. In divalent cation‐free external solution two additional currents were activated: an inwardly rectifying hyperpolarization‐activated current, IHA, and a depolarization‐activated current, IDA. I HA and IDA could be carried by several monovalent cations; the sizes of currents in descending order were: K+ > Cs+ > Na+ for IHA and Na+ > K+ >> Cs+ for IDA. IHA was activated and deactivated instantaneously and showed no inactivation whereas IDA was activated, inactivated and deactivated within tens of milliseconds. These currents were inhibited by external calcium with an IC50 of 0.3 μm for IDA and an IC50 of 20 μm for IHA. Cyclopiazonic acid (CPA) induced an outward, but not an inward current. SK&F 96365, a blocker of store‐operated Ca2+ channels, suppressed IDA with a half‐maximal inhibitory concentration of 9 μm but was ineffective in inhibiting IHA at concentrations up to 100 μm. Gd3+ and La3+ strongly suppressed IDA at 1 and 10 μm, respectively and were less effective in blocking IHA (complete inhibition required a concentration of 100 μm for both). Carbachol at 10–100 μm evoked about a 3‐fold increase in IHA amplitude and completely abolished IDA. We conclude that IHA and IDA are Ca2+‐blockable cationic currents with different ion selectivity profiles that are carried by different channels. IDA shows novel voltage‐dependent properties for a cationic current.