An inwardly rectifying potassium channel in the basolateral membrane of sheep parotid secretory cells.

Using whole-cell patch-clamp techniques, we demonstrate that sheep parotid secretory cells have both inwardly and outwardly rectifying currents. The outwardly rectifying current, which is blocked by 10 mmol/liter tetraethylammonium (TEA) applied extracellularly, is probably carried by the 250 pS Ca(2+)- and voltage-activated K+ (BK) channel which has been described in previous studies. In contrast, the inwardly rectifying current, which is also carried by K+ ions, is not sensitive to TEA. It is similar to the inwardly rectifying currents observed in many excitable tissues in that (i) its conductance is dependent on the square root of the extracellular K+, (ii) the voltage range over which it is activated is influenced by the extracellular K+ concentration and (iii) it is blocked by the addition of Cs+ ions (670 mumol/liter) to the bathing solution. Our previously published cell-attached patch studies have shown that the channel type most commonly observed in the basolateral membrane of unstimulated sheep parotid secretory cells is a K+ channel with a conductance of 30 pS and, in this study, we find that its conductance also depends on the square root of the extracellular K+ concentration. It thus seems likely that it carries the inwardly rectifying K+ current seen in the whole-cell studies.

Cation channels in basolateral membranes of sheep parotid secretory cells.

We observed 240-pS K+ channels in 63% of cell-attached patches, and 30-pS K+ channels were observed in 95% of cell-attached patches. The 240-pS K+ channel had the relative permeability sequence of K+ (1) = Rb+ (1) > Cs+ (0.3) >> Na+ (0.03) and the relative conductance sequence of K+ (1) > Rb+ (0.22) > Cs+ (0.05) > Na+ (0). It was activated by intracellular free Ca2+ and by depolarization. It was blocked by 10 mmol/l tetraethylammonium (TEA) applied extracellularly. The 30-pS K+ channel had the relative permeability sequence of K+ (1) = Rb+ (1) > Cs+ (> Na+ (< 0.09) and the relative conductance sequence of K+ (1) > Rb+ (0.45) > Cs+ (0) = Na+ (0). Its activity was not sensitive to cytosolic free Ca2+ or membrane potential, and it was not blocked by 10 mmol/l TEA extracellularly. Acetylcholine (10 mumol/l) activated the 240-pS voltage-activated and Ca(2+)-activated K+ channels but did not activate the 30-pS K+ channels. We conclude that the 30-pS K+ channel probably determines the properties of the basolateral membrane in unstimulated sheep parotid secretory cells, whereas the 240-pS voltage-activated and Ca(2+)-activated K+ channel may be important during parasympathomimetic stimulation.

Tetraethylammonium blocks muscarinically evoked secretion in the sheep parotid gland by a mechanism additional to its blockade of BK channels.

Since the secretory cells of the sheep parotid gland contain large numbers of high-conductance, voltage- and Ca(2+)-activated K+ channels (BK channels), we have used tetraethylammonium (TEA), a commonly employed blocker of BK channels, to investigate their role in secretion by this gland. In patch-clamp studies we found that 10 mmol/l TEA applied extracellularly inhibits the BK channel but not a 30-pS K+ channel also seen in this gland. We then showed by in-vivo perfusion that muscarinically evoked secretion is inhibited almost completely by 10 mmol/l TEA. We next used microspectrofluorimetry with fura-2 to demonstrate that muscarinic agonists cause the intracellular free Ca2+ concentration to increase. Unexpectedly, however, we found that 0.3-10 mmol/l TEA inhibited the increase in intracellular free Ca2+ induced by 5.0 mumol/l bethanechol or by 0.1 mumol/l acetylcholine. Consequently we conclude that the inhibition of muscarinically evoked secretion by the sheep parotid gland by TEA cannot be attributed solely to blockade of the BK channel--rather it must be attributed, at least in part, to blockade of some step in muscarinic signal transduction, for instance, receptor-agonist binding or Ca2+ release into the cytosol.

A 23-pS Ca2(+)-activated K+ channel in MCF-7 human breast carcinoma cells: an apparent correlation of channel incidence with the rate of cell proliferation.

In studies on the apical membranes of cultured MCF-7 human breast carcinoma cells, we found two conspicuous K+ channel types with conductances of 23 and 70 pS, respectively. Of these, the 23-pS K+ channel was most conspicuous. In cell-attached patches with KCl in the pipette, it had a linear current/voltage (I/V) relation and was activated by depolarisation and in excised inside-out patches it was highly selective for K+ over Na+ (permeability ratio of Na+ to K+, PNa/PK = 0.02). Rubidium (Rb+) had a similar permeability to K+, although it was only conducted at 20% of the rate of K+, and cesium (Cs+) had a permeability less than 30% that of K+ and was not conducted at all. Both Cs+ and Rb+ acted as partial blockers when applied internally but the channel was not blocked by external tetraethylammonium (TEA, 10 mmol/l), quinidine (200 mumol 1) or apamin (50 nmol/l). It was activated by Ca2+ in the range 10(-7)-10(-6) mol/l. In cell-attached patches at a pipette potential of O mV, the open-time histogram was described by a single exponential (time constant 1.6 ms) and the closed-time histogram by two exponentials (time constants 0.5 and 1.5 ms). The incidence of the 23-pS but not the 70-pS channel depended on the rate of cell proliferation. Thus, in studies on cell-attached patches from cells in the exponential growth phase, the 23-pS channel was observed in 78% of patches.(ABSTRACT TRUNCATED AT 250 WORDS)

Concordance between colonic myoelectrical signals recorded with intramuscular electrodes in the human rectosigmoid in vivo.

The myoelectrical activity of the human rectosigmoid colon was studied simultaneously in six subjects at two sites using two pairs of fine wire bipolar electrodes. The electrodes were spaced 2-5 cm apart in the rectosigmoid after insertion into the smooth muscle layers under direct vision at sigmoidoscopy. The electrodes were implanted at positions between 8 and 25 cm from the anal verge in different subjects. The frequency of myoelectrical burst activity together with the burst duration recorded by each electrode pair was examined. The relation of burst frequency and burst duration in the higher and lower placed electrodes was also assessed. In none of the subjects was three evidence of synchrony between the electrode pairs. In addition, there was no relation between the relative position of the electrodes and the intrinsic frequency of duration of myoelectrical bursts. It is concluded that regions of smooth muscle in the unstimulated human colon in vivo act independently and that there is no effective common neuromuscular drive under these conditions.

Human rectosigmoid electromyography: a new approach and some pitfalls.

A method has been developed to record directly myoelectrical activity from the smooth muscle of the colon of intact subjects using pairs of intramuscular wires. Discrete bursts of myoelectrical activity occurred at 4-20 per min. A small interelectrode distance in this method allows contamination of colonic myoelectrical activity by the electromyogram of skeletal muscle to be excluded. This artefact has not been considered in previous recordings of 'colonic' activity.

Herpes simplex and duodenal ulcer pathology.

An association between Herpes simplex Virus 1 (HSV-1) and duodenal ulcer disease has been suggested. Duodenal ulcers, like HSV-1 lesions, exhibit periodicity in recurrence. Several of the presently available anti-ulcer agents may have an antiviral action. Antibody titres in some studies have shown selective increases to HSV-1 in duodenal ulcer patients. The aim of this study was to determine whether a real association exists between HSV-1 and endoscopically proven duodenal ulcer or duodenal erosive disease. In a prospective study, 27 patients with either duodenal ulcer (16) or duodenal erosions (11) were studied in order to attempt isolation of HSV-1. Acute and convalescent sera were also taken and examined by an enzyme linked-immunoabsorbent assay system for antibody titres to HSV-1. Duodenal biopsies from a further 26 patients with duodenal ulcer or erosive disease were also examined retrospectively for HSV-1 by the immunoperoxidase technique. In no case of either duodenal ulcer or duodenal erosive disease was HSV-1 isolated by any of the above methods, nor was a relationship demonstrated by acute or convalescent HSV-1 antibody titres. Hence, this study does not support an association between HSV-1 and duodenal ulcer or erosive disease.