Pancreatic α-cells exhibit oscillations in cytosolic Ca2+ (Ca2+c), which control pulsatile glucagon (GCG) secretion. However, the mechanisms that modulate α-cell Ca2+c oscillations have not been elucidated. As β-cell Ca2+c oscillations are regulated in part by Ca2+-activated K+ (Kslow) currents, this work investigated the role of Kslow in α-cell Ca2+ handling and GCG secretion. α-Cells displayed Kslow currents that were dependent on Ca2+ influx through L- and P/Q-type voltage-dependent Ca2+ channels (VDCCs) as well as Ca2+ released from endoplasmic reticulum stores. α-Cell Kslow was decreased by small-conductance Ca2+-activated K+ (SK) channel inhibitors apamin and UCL 1684, large-conductance Ca2+-activated K+ (BK) channel inhibitor iberiotoxin (IbTx), and intermediate-conductance Ca2+-activated K+ (IK) channel inhibitor TRAM 34. Moreover, partial inhibition of α-cell Kslow with apamin depolarized membrane potential ( Vm) (3.8 ± 0.7 mV) and reduced action potential (AP) amplitude (10.4 ± 1.9 mV). Although apamin transiently increased Ca2+ influx into α-cells at low glucose (42.9 ± 10.6%), sustained SK (38.5 ± 10.4%) or BK channel inhibition (31.0 ± 11.7%) decreased α-cell Ca2+ influx. Total α-cell Ca2+c was similarly reduced (28.3 ± 11.1%) following prolonged treatment with high glucose, but it was not decreased further by SK or BK channel inhibition. Consistent with reduced α-cell Ca2+c following prolonged Kslow inhibition, apamin decreased GCG secretion from mouse (20.4 ± 4.2%) and human (27.7 ± 13.1%) islets at low glucose. These data demonstrate that Kslow activation provides a hyperpolarizing influence on α-cell Vm that sustains Ca2+ entry during hypoglycemic conditions, presumably by preventing voltage-dependent inactivation of P/Q-type VDCCs. Thus, when α-cell Ca2+c is elevated during secretagogue stimulation, Kslow activation helps to preserve GCG secretion.

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487 Background: Positive surgical margins with radical cystectomy for invasive urothelial cancer are associated with adverse prognosis. In non-metastatic patients, adjuvant radiation therapy (ART) is sometimes employed for patients with positive margins or locally advanced stage. However, evidence for benefit of ART in these patients to improve survival is limited. In this study, using a national database we investigate the factors associated with use of ART and its impact of the overall survival. Methods: National Cancer Database was queried for patients who underwent radical cystectomy from 2004-2013 for invasive urothelial cancer. Inclusion criteria were urothelial histology, pT2 stage with positive surgical margins or ³pT3 , and no evidence metastasis. Patients with regional or distant metastasis or patient who underwent adjuvant chemotherapy were excluded. Univariate and multivariate analysis performed to assess the factors associated with the use of ART. Overall survival was compared using log rank test. Results: In total, 18,828 patients met the inclusion criteria, of which 359 (1.91%) underwent ART. Mean duration between radical cystectomy and ART was 4.4 months. On univariable analysis, Black or Hispanic race, Medicare/Medicaid insurance status, treatment at community health center, ileal conduit diversion, advanced pathological stage (pT3/T4) were associated with higher use of ART (all p<0.005). On multivariate analysis community health facility and adequate lymph node dissection (>10 lymph nodes excision) were associated with use of ART (all p<0.05) (see table). The use of ART was not associated with improved overall survival. Conclusions: The utilization of ART after radical cystectomy for urothelial carcinoma is low. The benefit of ART on the overall survival is not clear and would need further investigation. [Table: see text]