SnapFib: An easy build Arduino based tabletop prototype for thin film deposition by Successive Ionic Layer Adsorption and Reaction method

Non-vacuum-based techniques are suitable for thin-film deposition with precision stoichiometric control. Among those, the Successive Ionic Layer Adsorption and Reaction (SILAR) method is gaining popularity for its aqueous-based almost room temperature deposition option. This method has many advantages, including the ability to control the elemental composition and stoichiometry of precursors. It is also suitable for large-area deposition. It has many runtime parameters, e.g., the number of cycles, dip time, rinse time, etc., that control the quantitative and qualitative physical properties of the deposited film. But manually controlling all these parameters for the whole process is very difficult and cumbersome. Although there are several reports published on this similar type of home-built prototype, for fast, accurate, and economically affordable deposition operations, we need to develop a machine that maintains all the properties of the SILAR process and can be made using cheap technologies. Here we report the SnapFib, a cost-effective automated tabletop prototype machine that is easy to build for thin-film deposition on soda-lime glass substrates by the SILAR method without almost any human intervention. SnapFib is built using linear actuators, an ATmega328P (a microcontroller available on Arduino boards), and some other parts collected from laboratory sites. The whole firmware needed for this device has been developed and maintained using the Arduino IDE (Integrated Development Environment). All required functional features and control parameters are encoded in the microcontroller firmware. The construction cost of this prototype is around 600 USD. We validated our construction through XRD (X-ray Diffraction) and FESEM (Field Emission Scanning Electron Microscope) characterizations of thin films that were deposited by SnapFib. Since this is built under the CC-BY license, students and researchers can freely perform and validate their experiments and modify the hardware and software as required. With how easy it is to make and how much it costs; we hope that many thin-film deposition labs will quickly start using SnapFib as an added benefit.

The Impact of Health Sector Reforms on Health System in Bangladesh: A Scoping Review

Background

Climate-induced environmental changes, and their potential impact on population health, are among the most pressing challenges affecting health systems. These health impacts put additional strain on health systems, putting their resilience and capacity to deal with increased shocks and stresses to the test. Implementing reforms to address the vulnerabilities in the health system can help build its capacity to cope with these shocks. We conducted a scoping review to explore the literature on health sector reforms in Bangladesh and understand their impact on health systems.

Methods

A scoping review was conducted by searching through academic (MEDLINE, SCOPUS, Web of Science and Google Scholar) and grey literature published in English and French between 1991 and 2021 that addressed national health sector reforms impacting the health system and access to care.

Results

Our search yielded 2688 articles for screening and 22 were included in our scoping review. One of the major health sector reforms was the shift from a project-based approach to a sector-wide approach (SWAp) in health. Studies found that implementing initiatives such as community clinics, a voucher scheme for pregnant women, increase in hospital beds at public facilities improved health care access and delivery of care, especially for rural districts. Despite government efforts, the health system continues to be vulnerable to shocks due to a significant shortage of formally qualified health professionals especially nurses and technologists and relatively low public financing.

Conclusions

Evidence suggests that health sector reforms implemented as part of SWAp have had a limited improvement on the health system. More emphasis should be placed in the future on implementing reforms to address critical issues such as human resources for health and health financing, which may contribute to building their capacity to cope with emerging threats due to climate change and improving access to care.

Key messages

Building a resilient health system may involve assessing the system's vulnerabilities, strengths and limitations through the perspective of health sector reforms. Current health sector reforms have had limited impact in addressing the vulnerabilities of the health system.

Probing the magnetic ground state of single crystalline Ce3TiSb5

Motivated by the report of superconductivity in R₃TiSb₅ (R  =  La and Ce) and possibly Nd₃TiSb₅ at  ∼4 K, we grew single crystals of La₃TiSb₅ and Ce₃TiSb₅ by the high-temperature solution method using Sn as a flux. While in both compounds we observed a superconducting transition at 3.7 K for resistivity and low-field magnetization, our data conclusively show that it arose from residual Sn flux present in the single crystals. In particular, the heat capacity data do not present any of the anomalies expected from a bulk superconducting transition. The anisotropic magnetic properties of Ce₃TiSb₅, crystallizing in a hexagonal P6₃/mcm structure, were studied in detail. We find that the Ce ions in Ce₃TiSb₅ form a Kondo lattice and exhibited antiferromagnetic ordering at 5.5 K with a reduced moment and a moderately normalized Sommerfeld coefficient of 598 mJ/mol K². The characteristic single-ion Kondo energy scale was found to be  ∼8 K. The magnetization data were subjected to a crystal electric field (CEF) analysis. The experimentally observed Schottky peak in the 4f-electron heat capacity of Ce₃TiSb₅ was reproduced fairly well by the energy levels derived from the CEF analysis.

Evaluation of splicing efficiency in lymphoblastoid cell lines from patients with splicing-factor retinitis pigmentosa

PURPOSE

Retinitis pigmentosa (RP) is caused by mutations in a variety of genes, most of which have known functions in the retina. However, one of the most perplexing findings of recent retinal genetics research was the discovery of mutations causing dominant RP in four ubiquitously expressed splicing factors. The aim of this study was to use lymphoblast cell lines derived from RP patients to determine whether mutations in two of these splicing factors, PRPF8 and PRPF31, cause measurable deficiencies in pre-mRNA splicing.

METHODS

cDNA was prepared from lymphoblastoid cell lines derived from RP patients bearing mutations in the splicing factor genes and controls, grown under a variety of conditions. Introns representing the U2 and U12 intron classes, with both canonical and noncanonical donor and acceptor sequences, were analyzed by real-time PCR to measure the ratio of spliced versus unspliced transcripts for these introns. In addition, plasmids encoding the retinal outer segment membrane protein-1 (ROM-1; exon 1 to exon 2) gene, both in the wild-type form and with mutations introduced into the splice donor sites, were transfected into cell lines. The spliced versus unspliced cDNA ratios were measured by real-time RT-PCR.

RESULTS

Splicing of four canonical U2 introns in the actin beta (ACTB), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), PRPF8, and retinitis pigmentosa GTPase regulator (RPGR) genes was unaffected in PRPF8 mutant cells. However, the splicing efficiency of RPGR intron 9 was significantly decreased in PRPF31 mutant cell lines. In contrast, a consistent decrease in the splicing efficiency of all U12 and noncanonical U2 introns was seen in PRPF8, but not in PRPF31, mutant cells, with statistical significance for STK11 intron 3.

CONCLUSIONS

In spite of the ubiquitous expression patterns of the genes implicated in splicing factor RP, no pathology has yet been documented outside the retina. The observed differences in splicing efficiency described herein favor the hypothesis that these mutations may have a subpathological effect outside the retina. These observations argue against a defect in some yet to be discovered additional function of these proteins and support the alternative hypothesis that this form of RP does indeed result from aberrant splicing of retinal transcripts.

Anencephaly and pregnancy outcome in Iran

OBJECTIVES

The aim of this research is to study the complications of pregnancy associated with anencephaly.

STUDY METHODS

Thirty-five mothers who delivered an anencephalic baby (as a case group) and forty-three mothers who delivered a non-anencephalic baby (as a control group)were included in this analytical research study. All cases and controls had singleton pregnancies. More than one matched control was chosen for each case when possible. The cases were selected by a survey of 149,000 births in six educational centers located in Tehran. The control group matched with the study group regarding birth date, maternal age, socioeconomic status and living environment. The outcomes for the control and study groups were studied and compared in the following areas: premature rupture of membrane, pregnancy length, fetal presentation, hydramnios, fetal death, sex ratio (male to female ratio) and other anomalies.

RESULTS

Anencephaly increased the likelihood of premature rupture of membrane by a factor of seven (p < 0.001). Pre-term birth was six times more likely (p < 0.005) and acephalic fetal presentation was 46% (p < 0.0005). In the study group, sex ratio was 0.52 and in control was 1.68 (p < 0.025). Further, hydramnios appeared in 90% of the study group. Finally, the general likelihood of any abnormality was 19 times (p < 0.0005) greater in the study group than the control group.

CONCLUSIONS

Considering the clear correlation between anencephaly and pregnancy complications, precise prenatal care, early diagnosis and treatment are strongly indicated in order to avoid serious maternal complications.

Cytotrophoblast stem cell lines derived from human embryonic stem cells and their capacity to mimic invasive implantation events

BACKGROUND

An effective embryonic-maternal interaction is crucial for successful human pregnancy. Failure of this process is a major cause of infertility and can lead to placental dysfunction resulting in recurrent miscarriage, fetal retardation and pre-eclampsia. Research is severely constrained by ethical and practical considerations; therefore, we aimed to generate cytotrophoblast stem (CTBS) cell lines from human embryonic stem cells (HESCs).

METHOD

Beta-HCG was used as a marker of viable trophoblast cells. In defined culture, embryoid bodies were generated from HESCs and selected for trophoblast enrichment by rounds of cellular aggregation and disaggregation. Distinct CTBS cell lines were isolated and characterized. Spheroid cytotrophoblast bodies were generated and their interaction with luteal-phase endometrial stroma was analysed by real-time image analysis.

RESULTS

Three CTBS cell lines were derived, which were maintained in the absence of residual HESCs, fibroblast feeder cells or extracellular matrix. CTBS cells displayed typical cytotrophoblast and syncytiotrophoblast characteristics and exhibited further differentiation to invasive endovascular cell phenotype. One cell line was generated with constitutive expression of enhanced green fluorescent protein (eGFP). Spheroid trophoblast bodies mimicked closely the early invasive stages of implantation when incubated with human endometrial stromal preparations in vitro.

CONCLUSION

These human CTBS cell lines are a significant new model for investigating human placentation and may have considerable potential in cell therapy applications.

The revival of surgical treatment for isolated proximal high grade LAD lesions by minimally invasive coronary artery bypass grafting

BACKGROUND

Percutaneous coronary angioplasty (PTCA) and stent implantation have become the first-line intervention for patients with isolated proximal LAD-lesions. Minimally invasive direct coronary artery bypass surgery (MIDCAB) has recently been developed to reduce surgical invasiveness for single LAD revascularization. This study focus on the question whether MIDCAB could be an alternative treatment for isolated proximal LAD lesions.

METHODS

Starting in 1996, MIDCAB was performed in 618 patients. Angiography was performed before discharge and repeated after 6 months at follow-up examination. In an ongoing randomized trial 150 patients with an indication for treatment of a LAD lesion have been included to compare the mid-term outcome after PTCA (n=79) vs. MIDCAB (n=71).

RESULTS

In 618 MIDCAB procedures 30-day mortality was 0.6%, perioperative myocardial infarction rate was 1.6%. The conversion rate to sternotomy was 3.4%. The learning curve was demonstrated by a patency rate of 96.0% in 1997, 98.0% in 1998 and 99.1% in 1999, respectively. At 6 months patency rate was 94.4% in 1997 and 97.0% in 1998. The rate of severe stenosis >75% dropped from 5.4% in 1997 to 3.4% in 1998. The over all rate of reinterventions was 5.6%. The preliminary result of the randomized trial revealed a difference in the number of perioperative adverse events, 11.4% in the MIDCAB group vs. 6.3% in the PTCA group (P<0.05). At 6 months follow-up 88. 7% of the MIDCAB patients were free from angina vs. 58.2% of the PTCA patients (P<0.02). Restenosis and a positive stress test was diagnosed in 27.9% of the PTCA patients vs. 8.4% of the MIDCAB patients (P<0.02). Reintervention was necessary in 27.9% of the patients after PTCA vs. 8.4% of the patients after MIDCAB.

CONCLUSION

MIDCAB is a safe and effective but technically demanding procedure. Perioperative adverse events may be expected, but early as well as mid-term patency rate are good. When compared to PTCA, the freedom from angina and the need for additional revascularization procedures after 6 months is statistically better for patients having MIDCAB surgery. Thus, MIDCAB is considered a valuable alternative for isolated proximal high grade LAD lesions.

Quality assessment in minimally invasive coronary artery bypass grafting

OBJECTIVES

The most important determinant for the success of minimally invasive coronary artery bypass grafting (MIDCAB) is the quality and long-term patency of the graft and anastomosis. Intra and postoperative quality assessment is important to confirm the safety and effectiveness of minimally invasive techniques.

METHODS

From January to December 1998 MIDCAB was performed in 246 patients using a limited minithoracotomy for single left anterior descending artery (LAD) revascularization. According to our standard protocol quality assessment of the graft and anastomosis consisted of intraoperative flow measurement, early postoperative angiography and follow-up angiography after 6 months.

RESULTS

Intraoperative flow measurement was performed in patients with anastomoses unsuitable for coronary probing (75/246, mean flow of 34.3 +/- 17.7 ml/min). Early patency was confirmed by intraoperative monoplane angiogram in 37/246 (15.0%) patients and by postoperative multiplan angiography in 205/246 (83.3%). Early patency rate was 98.0%. Six months follow-up showed a patency rate of 97.5% (one occluded graft, two severe and two moderate stenoses at the anastomotic site). Eighty-nine percent of the patients were in a CCS angina class I, 11% in class II, respectively. Six months mortality was 0.8%. Re-intervention had to be performed in 5/116 (4.3%).

CONCLUSIONS

A standardized protocol for quality assessment is mandatory for MIDCAB surgery. The proposed algorithm serves to ensure the safety and effectiveness of this new technique. Our recent series document an excellent outcome of the MIDCAB approach. Postoperative multiplan angiography is the only technique to achieve valid information about the quality of graft and anastomosis.

Indication and patient selection in minimally invasive and òff-pump' coronary artery bypass grafting

BACKGROUND

The selection criteria to perform 'off-pump' coronary bypass (OPCAB) grafting are not well defined. The aim of this presentation is to outline the indications and the patient selection on the basis of 2 years experience with 572 OPCAB procedures.

MATERIALS AND METHODS

From November 1996 minimally invasive coronary bypass grafting was performed in 406 patients using a limited minithoracotomy for single left anterior descending artery (LAD) revascularization (group A). In 166 patients full sternotomy and OPCAB grafting for single or multiple vessel revascularization was performed (group B).

RESULTS

In group A the procedure could be performed 'off-pump' together with a limited thoracotomy in 406 out of 457 patients (88.8%) who were scheduled for single graft revascularization to LAD. Exposure and quality of the LAD was good in 308/406 (76.0%) of the patients. The decision for sternotomy was made for different preoperative characteristics of these patients: Obese female patients 16/457 (3.5%), angiographic evidence of an intramyocardial running LAD 6/457% (1.4%), diffusely diseased and small LAD 11/457 (2.4%) severe COPD 3/457 (0.7%), unstable angina 11/457 (2.4%), emergency revascularization after failed PTCA 4/457 (0.8%). In 315/406 (77.8%) of the minimally invasive direct coronary artery bypass (MIDCAB)-patients exposure and quality of the LAD was good, in 97/406 (22.2%) moderate or even bad. In the latter subgroup stenosis free anastomosis was reduced (86.5%) compared to the subgroup of good exposure and quality with 98.3%. In group B selection for sternotomy and 'off-pump' procedure was made in 117/166 (70.4%) patients with a normal preoperative status (stable angina, ejection fraction > 35%) and with coronary lesions amenable for beating heart surgery (proximal RCA lesion > 80%, not calcified and well defined POD and marginal branches). In 49/166 (29.5%) decision for 'off-pump' procedure was made on the basis of a potential risk for cardiopulmonary bypass (CPB) such as acute myocardial infarction in 10/166 (6.0%), reduced ventricular function with EF < 35 in 28/166 (16.9%), calcified ascending aorta 4/166 (2.4%) or concomitant diseases 7/166 (2.5).

CONCLUSION

To maintain excellent results after single LAD revascularization using the MIDCAB-approach, appropriate patient selection is crucial. Indication for sternotomy and 'off-pump' single LAD revascularization should made in those patients excluded for MIDCAB and in patients scheduled for multiple vessel-CABG who are at high risk for CPB (concomitant pulmonary, renal, neurological diseases or severely impaired left ventricular dysfunction) and have suitable target coronary arteries in term of location and quality.

Angiographic results after minimally invasive coronary bypass grafting using the minimally invasive direct coronary bypass grafting (MIDCAB) approach

OBJECTIVE

The aim of the study was to evaluate the early and mid-term angiographic results after minimally invasive coronary bypass grafting using an 'off-pump' technique via a lateral minithoracotomy.

METHODS

In 221 out of 271 patients (81.5%) who underwent minimally invasive direct coronary bypass grafting (MIDCAB) the quality of the internal thoracic artery (ITA)-graft and the anastomosis was evaluated by conventional coronary angiography between the 2nd and 6th postoperative day (POD). A subgroup of 130 patients (47.9%) of the initial cohort were repeatedly controlled by angiography 6 months later.

RESULTS

The early postoperatively patency rate of the grafts was (96.8%). Moderate anastomotic stenosis between 50 and 75% was found in 13/221 (5.8%) patients, whereas severe stenosis of more than 75% was seen in 10/221 (4.5%) and occlusion of the graft in 3/221 (1.3%) patients. A stress-ECG was performed in patients with a severe stenosis to provoke ST-segment changes or clinical findings of myocardial ischemia. A positive stress test was found in 4/221 patients (1,8%). Early re-intervention was required in 7/221 (3.1%) patients. After 6 months, angiographic follow-up revealed a patency rate of (95.4%). Of 130 patients 5 (3.8%) presented with moderate anastomotic stenosis, whereas 3/130 (2.0%) patients showed a severe stenosis with one patient (0.7%) having myocardial ischemia during stress test. Occlusion of the graft was seen in 3/130 patients (2.3%). During follow-up, 4/130 (3.0%) patients underwent re-intervention. A comparison between early postoperative and 6-months angiogram revealed a decrease or a disappearance of the severity of the stenosis in 4/15 patients (26.6%).

CONCLUSION

Since stenosis of the anastomosis may occur after minimally invasive, beating heart coronary bypass grafting, postoperative angiography should be performed to provide quality control and to guide appropriate further treatment. The latter is necessary if the stenosis is accompanied by reduced run-off and evidence of myocardial ischemia during stress test. An improvement of early stenosis at the anastomosis may be expected in more than 25%.

Coronary bypass grafting without cardiopulmonary bypass--technical considerations, clinical results, and follow-up

BACKGROUND

Coronary bypass surgery can be performed less invasively by avoiding cardiopulmonary bypass (CPB). We present our early 'off pump' coronary bypass surgery experience in combination with a minithoracotomy or sternotomy.

METHODS

Between 11/1996 and 12/1997 312 patients were included in a prospective study, 223 (Group A) underwent an antero-lateral minithoracotomy (MIDCAB) and 89 (Group B) had a full sternotomy (OPCAB). ITA harvesting and anastomosis was performed under direct vision in all cases. Different devices for local mechanical immobilization were used to perform the anastomosis.

RESULTS

In 212 patients of group A revascularization was by a single ITA graft and in 11 patients by a double graft using the radial artery as a T graft. Conversion to sternotomy and cardiopulmonary bypass was necessary in 12 (5.3%) patients. Intraoperative myocardial infarction was observed in 5 patients (2.2%). Early-postoperative reoperation due to graft failure was necessary in 5 patients (2.2%). Mortality was 0.4% (one patient). The early postoperative graft patency rate was 97.1% as confirmed by angiography. In group B, 25 patients had single graft and 64 patients multiple graft revascularization. Intraoperative conversion to CPB was necessary in 10 patients (11.2%). Intraoperative myocardial infarction occurred in 1 patient (1.1%), postoperative low output syndrome in 2 patients (2.2%). Early postoperative reoperation due to graft failure was necessary in 1 patient (1.1%). Mortality was 1.1%. Angiographic control of 48 patients after 6 months confirmed a patency rate of 92.6%.

CONCLUSION

Coronary bypass surgery without using cardiopulmonary bypass is safe to achieve good early and mid-term results. MIDCAB is a minimally invasive technique. Experienced surgeons should be ready to compete with PTCA techniques.

Less-invasive coronary artery bypass grafting: different techniques and approaches

OBJECTIVE

The aim of this study was to compare four different techniques for less-invasive coronary artery bypass surgery with and without cardiopulmonary bypass (CPB) in terms of feasibility as well as in terms of the intra- and postoperative course.

METHODS

One hundred and fourteen patients were divided into four groups, according to the surgical technique. Group I: minithoracotomy, internal thoracic artery (ITA) harvesting and anastomosis under direct vision using cardiopulmonary bypass (CPB) on the fibrillating heart (n = 31). Group II: sternotomy and beating heart without CPB (n = 13). Group III: MIDCAB with CPB and cardioplegic cardiac arrest using endo-aortic balloon-occlusion, Port Access system (n = 9). Group IV: MIDCAB on the beating heart without CPB (n = 61). In total, 104 single and ten double graft procedures were performed using the radial artery T-graft technique in seven cases (groups III and IV).

RESULTS

Harvesting of the ITA graft took 41+/-16.2 min in group I and could be reduced to 31+/-8.3 min in group IV by the use of a specially-designed retractor. Complications were: death (n = 1, group I), myocardial infarction, (n = 1, group I), early occlusion of the graft (n = 1, group IV), early stenosis of the anastomosis (n = 2, groups I and IV), late stenosis of the anastomosis (n = 1, group IV), thrombosis of the femoral vein (n = 1, group III). Postoperative ventilation, ICU and hospital stay were similar among groups.

CONCLUSIONS

Based on our results, the following strategy has been developed: MIDCAB without CPB is the preferred technique for one-vessel graft procedures to the left anterior descendens (LAD) or RCA. The Port Access system (with CPB) is reserved as a second option for young patients requiring multiple-vessel grafting to the left coronary circulation (LAD/CX) and as a backup to avoid conversion. Sternotomy and an off-pump technique is used for single-vessel or multiple-vessel graft procedures in selected patients (emergency procedure, acute myocardial infarction, in the very obese).

Minimally invasive coronary artery bypass grafting without cardiopulmonary bypass: early experience and follow-up

BACKGROUND

There is renewed interest in coronary artery bypass grafting without cardiopulmonary bypass using the anterolateral minithoracotomy approach. We evaluated 209 patients who underwent minimally invasive direct coronary artery bypass grafting using an anterolateral minithoracotomy. The anastomosis was performed under direct vision on the beating heart without using cardiopulmonary bypass.

METHODS

The procedure was performed using a 6- to 9-cm left (or right) anterolateral thoracotomy for internal thoracic artery graft harvesting and anastomosis. Different devices were used for local immobilization. In 195 patients a single internal thoracic artery to left anterior descending coronary artery bypass was performed, in 3 patients a single right internal thoracic artery to right coronary artery bypass, and in 11 patients the radial artery was used together with the internal thoracic artery as a T-graft.

RESULTS

Conversion to sternotomy or cardiopulmonary bypass was necessary in 10 (4.7%) patients. Intraoperative myocardial infarction was observed in 4 patients (1.9%). Early postoperative redo operation was necessary in 5 patients (2.4%). Mortality was 0.47%. Postoperatively, 191 patients (91.3%) underwent angiography for graft patency control. The overall patency rate was 97.3%. Minor stenosis of the internal thoracic artery graft was observed in 18 patients (9.4%); moderate stenosis was observed in 5 patients (2.6%). Midterm angiographic follow-up after 6 months was performed in 58 patients. The patency rate was 98.2%. One patient with severe symptomatic stenosis (1.7%) underwent reoperation.

CONCLUSIONS

With the help of the local immobilization systems off-pump coronary artery bypass grafting was safely performed through a minithoracotomy. The incidence of intraoperative and postoperative complications was low and follow-up showed good results. Thus, minimally invasive direct coronary artery bypass grafting is an excellent technique for arterial revascularization in patients having symptomatic left anterior descending coronary artery disease.

Mechanism of delta pH maintenance in active and inactive cells of an obligately acidophilic bacterium

The acidophilic bacterium PW2 possessed a delta pH of ca. 1.9 and a delta psi of 0 mV, corresponding to a proton motive force (delta p) of--114 mV. Protonophore-treated cells possessed little delta p but a delta pH of ca. 1.5, as measured by salicylic acid distribution or pH measurement of cell lysates. Starving PW2 cells continued to possess a delta pH of ca. 1.7, but exhibited converse changes in delta psi and delta p, with the former rising to +80 to +100 mV and the latter dropping essentially to 0; progressive loss of respiration, cellular ATP, and culture viability accompanied these changes. Thus, the protonophore-treated or starving PW2 cells attained an H+ electrochemical equilibrium. Net H+ influx resulting from declining respiration probably accounted for the increased delta psi in these cells; indeed, when respiration was progressively inhibited in active cells, there was increasing transient H+ influx and a proportional increase in delta psi. This transient H+ influx was sufficient to lethally acidify the cytoplasm, but for a buffering capacity of 85 nmol of H+/mg of protein per pH unit. Thus, the linkage of the transient H+ influx with the rise in the delta psi and the cytoplasmic buffering capacity play central roles in acidophilism, and it is conceivable that the same impermeant cellular macromolecule(s) accounts for both. If so, the delta psi would be a Donnan potential that in active cells is offset by energy-dependent H+ extrusion.

Proton motive force and the physiological basis of delta pH maintenance in thiobacillus acidophilus

At optimal growth pH (3.0) Thiobacillus acidophilus maintained an internal pH of 5.6 (delta pH of 2.6 units) and a membrane potential (delta psi) of some +73 mV, corresponding to a proton motive force (delta p) of -83 mV. The internal pH remained poised at this value through external pH values of 1 to 5, so that the delta pH increased with decreasing external pH. The positive delta psi increased linearly with delta pH: above a delta pH of 0.6 units, some 60% of the increase in delta pH was compensated for by an opposing increase in delta psi. The highest magnitude of delta pH occurred at an external pH of 1.0, where the cells could not respire. Inhibiting respiration by CN- or azide in cells at optimal pH decreased delta pH by only 0.4 to 0.5 units and caused a corresponding opposite increase in delta psi. Thus, a sizable delta pH could be maintained in the complete absence of respiration. Treatment of cells with thiocyanate to abolish the delta psi resulted in a time-dependent collapse of delta pH, which was augmented by protonophores. We postulate that T. acidophilus possesses unusual resistance to ionic movements. In the presence of a large delta pH (greater than 0.6 pH units), limited diffusion of H+ into the cell is permitted, which generates a positive delta psi because of resistance to compensatory ionic movements. This delta psi, by undergoing fluctuations, regulates the further entry of H+ into the cell in accordance with the metabolic state of the organism. The effect of protonophores was anomalous: the delta p was only partially collapsed, and respiration was strongly inhibited. Possible reasons for this are discussed.