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4,4'-Dithiocyanatostilbene-2,2'-disulfonic acid (DIDS), an inhibitor of the volume-sensitive anion channel, was used to investigate the role of this channel in the stimulation of rat pancreatic beta-cells by glucose and by tolbutamide. Glucose-stimulated electrical activity in beta-cells was markedly and reversibly inhibited by DIDS. The increase in cytosolic [Ca2+] and stimulated insulin release evoked by glucose were also inhibited by DIDS. In contrast to its inhibitory effect on glucose-induced beta-cell activity, DIDS had no effect on electrical activity, the rise in [Ca2+]i or insulin release induced by tolbutamide. DIDS failed to increase beta-cell input conductance, an index of whole-cell K(ATP) channel activity, or the rate of efflux of 86Rb+ from perifused islets, a measure of net K+ permeability. Furthermore, DIDS had no effect on intracellular pH or on regulatory volume increase following exposure of cells to hypertonic solutions, indicating that the effects of DIDS were not the result of inhibition of Cl- transport systems. It is suggested that the DIDS-induced repolarization is caused by inactivation of the volume-sensitive anion channel. The stimulation of beta-cell electrical and secretory activity by glucose, but not tolbutamide, may therefore involve activation of the anion channel. [ABSTRACT FROM AUTHOR]

Objectives: As plasma pH rises during pregnancy, the effect of raising external pH on spontaneous contractions in pregnant rat myometrium was investigated to test the hypothesis that elevated external pH depresses contraction.Study Design: Strips of longitudinal myometrium were loaded with SNARF (seminaphthorhodafluor) or Indo-1 for simultaneous intracellular pH or Ca++ and force measurements. Results were obtained from a minimum of five animals in each group, and significant differences were tested for by paired Student t tests.Results: Raising the external pH significantly reduced spontaneous force and calcium transient in the pregnant uterus. Raising the external pH led to a slow rise in intracellular pH, but this could not account for the functional effect. K+ rubidium 86-labeled efflux rates were unaffected by external pH, suggesting no hyperpolarization. The Ca++ channel agonist Bay K8644 (5 mumol/L) restored contractions abolished by raised external pH.Conclusions: Raised external pH reduces spontaneous contractions in the pregnant rat uterus, probably by an external effect on Ca++ entry. This effect may contribute to uterine quiescence before term. [ABSTRACT FROM AUTHOR]

Whey protein is a commonly ingested nutritional supplement amongst athletes and regular exercisers; however, its role in post-exercise rehydration remains unclear. Eight healthy male and female participants completed two experimental trials involving the ingestion of 35 g of whey protein (WP) or maltodextrin (MD) at the onset of a rehydration period, followed by ingestion of water to a volume equivalent to 150% of the amount of body mass lost during exercise in the heat. The gastric emptying rates of the solutions were measured using 13 C breath tests. Recovery was monitored for a further 3 h by the collection of blood and urine samples. The time taken to empty half of the initial solution (T 1/2 ) was different between the trials (WP = 65.5 ± 11.4 min; MD = 56.7 ± 6.3 min; p = 0.05); however, there was no difference in cumulative urine volume throughout the recovery period (WP = 1306 ± 306 mL; MD = 1428 ± 443 mL; p = 0.314). Participants returned to net negative fluid balance 2 h after the recovery period with MD and 3 h with WP. The results of this study suggest that whey protein empties from the stomach at a slower rate than MD; however, this does not seem to exert any positive or negative effects on the maintenance of fluid balance in the post-exercise period.

Effective assessment of laboratory practicals is a challenge for large-size classes. To reduce the administrative burden of staff members without compromising the student learning experience, we utilized dedicated computer software for short-answer question assessment for nearly 300 students and compared it with the more traditional, paper-based method of assessment of the same student cohort. Students were generally favorably disposed toward computer-assisted assessment (CAA): 75% of the students responded that for future assignments, they either had no preference for the method of assessment or would prefer CAA. Advantages were perceived to be remote access to the questions and ease of submission. The most common disadvantage cited was lack of internet access. Various advantages of CAA were mentioned by staff members: notably, the reduction in marking time and reduction of paperwork as well as the potential for the software to detect plagiarism and to administer anonymous marking. Disadvantages to CAA were the need to tailor questions to the technology, having to adapt to reading answers and marking onscreen, and the quality of feedback to students. All of the disadvantages could be overcome by training and improved versions of CAA software, currently under development. The use of CAA has proved to be a welcome addition to the tools available to staff members for the assessment of practical classes, and future improved versions of the software will increase the utility of this assessment method.

Exposure of insulin-secreting cells to hypotonic solutions causes cell swelling followed by regulatory volume decrease (RVD). We have previously demonstrated that RVD is due to activation of a Cl(-) conductance. The present study investigates whether changes in cytosolic [Ca(2+)] play a role in these responses. Hypotonic swelling of RINm5F insulinoma cells caused a marked increase in cytosolic [Ca(2+)]. This effect was abolished by omission of extracellular Ca(2+), by the Ca(2+) channel blockers D600 or Gd(3+)and by 4,4'-dithiocyanatostilbene-2,2'-disulphonic acid (DIDS), an inhibitor of the volume-sensitive anion. RVD was markedly impaired in the absence of extracellular Ca(2+), but not by D600 nor by Gd(3+). RVD was also inhibited by the maxi-K(+) (BK(Ca)) channel blockers tetraethylammonium (TEA) and iberiotoxin (IbTx), whereas the K(ATP) channel blocker tolbutamide was ineffective. Cell swelling was accompanied by activation of a K(+) conductance which was sensitive to TEA and IbTx but not to tolbutamide. It is concluded that cell swelling causes activation of the volume-sensitive anion channel, leading to depolarization and Ca(2+) entry via voltage-gated Ca(2+) channels. RVD is a Ca(2+)-dependent process, requiring low 'resting' levels of intracellular [Ca(2+)]. However, the swelling-induced increase in cytosolic [Ca(2+)] is not required for RVD to occur. RVD depends upon simultaneous activation of Cl(-) and K(+) channels. We suggest that the BK(Ca) channel is the major K(+) conductance involved in RVD.

1. Changes in relative cell volume in response to hypotonic solutions and glucose were studied in single isolated rat pancreatic beta-cells using a video-imaging technique. beta-cell electrical activity was recorded under similar conditions using the perforated patch technique. 2. Exposure of beta-cells to hypotonic solutions (10 and 33% hypotonicity) caused an immediate increase in cell volume to relative values of 1.09 and 1.33, respectively. This was followed by a gradual regulatory volume decrease. 3. Raising the concentration of glucose from 4 to 20 mM or 12 mM (with substitution of mannitol) increased beta-cell volume by 12 and 10%, respectively. This effect of glucose persisted when CO2+ was added to inhibit insulin release. Glucose-induced volume increases were sustained for the duration of exposure to elevated hexose concentration. The addition of 16 mM 3-O-methylglucose, which is transported into the beta-cell but not metabolized, produced only a transient 5% increase in beta-cell volume. 4. Exposure of beta-cells to a 15% hypotonic solution resulted in a transient depolarization and electrical activity. Raising the glucose concentration to 20 or 12 mM caused a sustained depolarization and generation of electrical activity. However, the addition of 16 mM 3-O-methylglucose had no effect on beta-cell membrane potential. The glucose-induced increase in volume and induction of electrical activity, when measured in single beta-cells simultaneously, showed comparable kinetics. 5. The secretion of insulin from intact pancreatic islets was stimulated by exposure to hypotonic solutions (10-33% hypotonicity). A 15% hypotonic solution stimulated insulin release to a peak value comparable to that elicited by raising the glucose concentration from 4 to 20 mM. Whereas hypotonic solutions caused a transient stimulation of insulin release, the effect of glucose was sustained. 6. It is suggested that glucose increases the volume in rat pancreatic beta-cells by a mechanism dependent upon metabolism of the sugar. The extent of cell swelling evoked by raised glucose concentrations is sufficient to depolarize the cells and induce electrical and secretory activity and may involve activation of a volume-sensitive anion conductance.