Polyurethane tubing

To maintain consistency with our prior work, glucose extraction measurements were performed with the rapid-sampling microdialysis (rsMD) system described previously.^{52 (link)} All other glucose measurements were performed with the continuous online microdialysis (coMD) system recently developed by Boutelle and coworkers (SI Figure 1 presents example calibration data for both systems).^{53 (link)} Briefly, needle-style microelectrodes for K⁺ and glucose were interfaced to the outlet line of the microdialysis probe with a 3D-printed microelectrode holder (SomosWaterShed XC 11122). As the glucose sensors are hand-made inhouse, there is variability in their performance. Only those sensors meeting practical performance metrics were used in these studies. The sensors used herein were those exhibiting a linear response (r²>0.99) over the concentration range of 50–1000 μM glucose with a sensitivity exceeding 0.5 pA/μM. In the case of microdialysis in animals, the fused silica outlet line was attached to the microelectrode holder with a 5-cm section of polyurethane tubing (0.18 mm ID × 0.36 mm OD: Instech Laboratories Inc.) to provide oxygen for glucose sensing. The clinical microdialysis catheters are constructed with polyurethane lines that were connected directly to the microelectrode holder.

Rats were implanted with a catheter into the jugular vein following the procedure detailed previously (Ding et al 2021 (link)). Briefly, rats were anesthetized with 2–3% isoflurane inhalation and a polyurethane tubing (I.D. × O.D. = 0.63 × 1.02mm; Instech Laboratories, Inc., Plymouth Meeting, PA, USA) was inserted into the right jugular vein. The remaining portion of the catheter coursed subcutaneously over the shoulder blade to exit the back of the rat via a 22-gauge cannula (Plastics One, Roanoke, VA, USA). Bupivacaine hydrochloride (Hospira, Inc., Lake Forest, IL, USA) at 0.25% and carprofen at 5 mg/kg (Zoetis Inc., Kalamazoo, MI, USA) were applied as analgesia during surgery. Catheters were flushed daily with ~0.5ml heparinized saline (20 IU/ml, Hospira, Inc., Lake Forest, IL, USA) containing 0.13 mg/ml gentamicin sulfate (McKesson, Livonia, MI, USA). Rats were checked once a week, typically after the Friday session, for catheter patency with intravenous administration of ~0.1ml of 10 mg/ml methohexital sodium (Par Pharmaceutical, Chestnut Ridge, NY, USA). Rats with failed catheters were excluded from further experiment and analysis.