The ruminal epithelium has an enormous capacity for the absorption of short-chain fatty acids (SCFAs). This not only delivers metabolic energy to the animal but is also an essential regulatory mechanism that stabilizes the intraruminal milieu. The epithelium itself, however, is endangered by the influx of SCFAs because the intracellular pH (pHi) may drop to a lethal level. To prevent severe cytosolic acidosis, the ruminal epithelium is able to extrude (or buffer) protons by various mechanisms: (i) a Na+/H+ exchanger, (ii) a bicarbonate importing system and (iii) an H+/monocarboxylate cotransporter (MCT). Besides pHi regulation, the MCT also provides the animal with ketone bodies derived from the intraepithelial breakdown of SCFAs. Ketone bodies, in turn, can serve as an energy source for extrahepatic tissues. In addition to SCFA uptake, glucose absorption has recently been identified as a potential way of eliminating acidogenic substrates from the rumen. At least with respect to SCFAs, absorption rates can be elevated when adapting animals to energy-rich diets. Although they are very effective under physiological conditions, the absorptive and regulatory mechanisms of the ruminal epithelium also have their limits. An increased number of protons during the state of ruminal acidosis can be eliminated neither from the lumen nor the cytosol, thus worsening dysfermentation and finally leading to functional and morphological alterations of the epithelial lining.

Due to intensive intracellular metabolism of short-chain fatty acids, ruminal epithelial cells generate large amounts of D-beta-hydroxybutyric acid, acetoacetic acid, and lactic acid. These acids have to be extruded from the cytosol to avoid disturbances of intracellular pH (pH(i)). To evaluate acid extrusion, pH(i) was studied in cultured ruminal epithelial cells of sheep using the pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Extracellular addition of D-beta-hydroxybutyrate, acetoacetate, or lactate (20 mM) resulted in intracellular acidification. Vice versa, removing extracellular D-beta-hydroxybutyrate, acetoacetate, or lactate after preincubation with the respective monocarboxylate induced an increase of pH(i). Initial rate of pH(i) decrease as well as of pH(i) recovery was strongly inhibited by pCMBS (400 microM) and phloretin (20 microM). Both cultured cells and intact ruminal epithelium were tested for the possible presence of proton-linked monocarboxylate transporter (MCT) on both the mRNA and protein levels. With the use of RT-PCR, mRNA encoding for MCT1 isoform was demonstrated in cultured ruminal epithelial cells and the ruminal epithelium. Immunostaining with MCT1 antibodies intensively labeled cultured ruminal epithelial cells and cells located in the stratum basale of the ruminal epithelium. In conclusion, our data indicate that MCT1 is expressed in the stratum basale of the ruminal epithelium and may function as a main mechanism for removing ketone bodies and lactate together with H+ from the cytosol into the blood.

This study sought to investigate effects of short-chain fatty acids and CO2 on intracellular pH (pHi) and mechanisms that mediate pHi recovery from intracellular acidification in cultured ruminal epithelial cells of sheep. pHi was studied by spectrofluorometry using the pH-sensitive fluorescent indicator 2',7'-bis (carboxyethyl)-5(6')-carboxyfluorescein acetoxymethyl ester (BCECF/AM). The resting pHi in N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES)-buffered solution was 7.37 +/- 0.03. In HEPES-buffered solution, a NH4+/NH3-prepulse (20 mM) or addition of butyrate (20 mM) led to a rapid intracellular acidification (P < 0.05). Addition of 5-(N-ethyl-N-isopropyl)-amiloride (EIPA: 10 microM) or HOE-694 (200 microM) inhibited pHi recovery from an NH4+/NH3-induced acid load by 58% and 70%, respectively. pHi recovery from acidification by butyrate was reduced by 62% and 69% in the presence of EIPA (10 microM) and HOE-694 (200 microM), respectively. Changing from HEPES-(20 mM) to CO2/HCO3(-)-buffered (5%/20 mM) solution caused a rapid decrease of pHi (P < 0.01), followed by an effective counter-regulation. 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS; 100 microM) blocked the pHi recovery by 88%. The results indicate that intracellular acidification by butyrate and CO2 is effectively counter-regulated by an Na+/H+ exchanger and by DIDS-sensitive, HCO3(-)-dependent mechanism(s). Considering the large amount of intraruminal weak acids in vivo, both mechanisms are of major importance for maintaining the pHi homeostasis of ruminal epithelial cells.

Plants, fungi and algae are important components of global biodiversity and are fundamental to all ecosystems. They are the basis for human well-being, providing food, materials and medicines. Specimens of all three groups of organisms are accommodated in herbaria, where they are commonly referred to as botanical specimens. The large number of specimens in herbaria provides an ample, permanent and continuously improving knowledge base on these organisms and an indispensable source for the analysis of the distribution of species in space and time critical for current and future research relating to global biodiversity. In order to make full use of this resource, a research infrastructure has to be built that grants comprehensive and free access to the information in herbaria and botanical collections in general. This can be achieved through digitization of the botanical objects and associated data. The botanical research community can count on a long-standing tradition of collaboration among institutions and individuals. It agreed on data standards and standard services even before the advent of computerization and information networking, an example being the Index Herbariorum as a global registry of herbaria helping towards the unique identification of specimens cited in the literature. In the spirit of this collaborative history, 51 representatives from 30 institutions advocate to start the digitization of botanical collections with the overall wall-to-wall digitization of the flat objects stored in German herbaria. Germany has 70 herbaria holding almost 23 million specimens according to a national survey carried out in 2019. 87% of these specimens are not yet digitized. Experiences from other countries like France, the Netherlands, Finland, the US and Australia show that herbaria can be comprehensively and cost-efficiently digitized in a relatively short time due to established workflows and protocols for the high-throughput digitization of flat objects. Most of the herbaria are part of a university (34), fewer belong to municipal museums (10) or state museums (8), six herbaria belong to institutions also supported by federal funds such as Leibniz institutes, and four belong to non-governmental organizations. A common data infrastructure must therefore integrate different kinds of institutions. Making full use of the data gained by digitization requires the set-up of a digital infrastructure for storage, archiving, content indexing and networking as well as standardized access for the scientific use of digital objects. A standards-based portfolio of technical components has already been developed and successfully tested by the Biodiversity Informatics Community over the last two decades, comprising among others access protocols, collection databases, portals, tools for semantic enrichment and annotation, international networking, storage and archiving in accordance with international standards. This was achieved through the funding by national and international programs and initiatives, which also paved the road for the German contribution to the Global Biodiversity Information Facility (GBIF). Herbaria constitute a large part of the German botanical collections that also comprise living collections in botanical gardens and seed banks, DNA- and tissue samples, specimens preserved in fluids or on microscope slides and more. Once the herbaria are digitized, these resources can be integrated, adding to the value of the overall research infrastructure. The community has agreed on tasks that are shared between the herbaria, as the German GBIF model already successfully demonstrates. We have compiled nine scientific use cases of immediate societal relevance for an integrated infrastructure of botanical collections. They address accelerated biodiversity discovery and research, biomonitoring and conservation planning, biodiversity modelling, the generation of trait information, automated image recognition by artificial intelligence, automated pathogen detection, contextualization by interlinking objects, enabling provenance research, as well as education, outreach and citizen science. We propose to start this initiative now in order to valorize German botanical collections as a vital part of a worldwide biodiversity data pool.

Short-chain fatty acids are absorbed in considerable amounts from the rumen. During transit through the epithelial layer, they are intensively metabolised. Interaction between intraepithelial metabolism and absorption, however, is hardly understood. The present study therefore compared the transepithelial transport of the easily metabolised n-butyrate with that of the more metabolism-resistant iso-butyrate both under in vivo conditions (isolated and washed reticulorumen) and in vitro conditions (Ussing chamber). Under in vivo conditions, net absorption of n-butyrate was significantly higher than that of iso-butyrate. The in vitro experiments showed that the higher net flux of n-butyrate was solely due to a higher mucosal-to-serosal flux, whereas the serosal-to-mucosal flux of butyrate was independent from the isoform. Blocking intraepithelial ATP delivery by 2,4-dinitrophenol abolished the net flux of n-butyrate. The study indicates that metabolism and/ or ATP availability stimulates n-butyrate net absorption. By this, the metabolic activity of the epithelium may have a regulatory influence on absorption of n-butyrate.