analysis ͉ dispersion ͉ flow ͉ microscale ͉ pulse

Glucose-induced β-cell action potential (AP) repolarization is regulated by potassium efflux through voltage gated (Kv) and calcium activated (K Ca ) potassium channels. Thus, ablation of the primary Kv channel of the β-cell, Kv2.1, causes increased AP duration. However, Kv2.1 −/− islet electrical activity still remains sensitive to the potassium channel inhibitor tetraethylammonium. Therefore, we utilized Kv2. −/− mouse islet AP repolarization. Inhibition of SK channels decreased AP firing frequency by 66% and increased AP duration by 67% only when Kv2.1 is ablated or inhibited and enhanced GSIS by 2.7-fold. Human islets also express SK3 channels and their β-cell AP frequency is significantly accelerated by 4.8-fold with apamin. These results uncover important repolarizing roles for both Kv and K Ca channels and identify distinct roles for SK channel activity in regulating calcium-versus sodium-dependent AP firing.

Adhesion and degranulation promoting adapter protein (ADAP), a positive regulator of T cell receptor (TCR) signaling, is required for thymocyte development and T cell homeostasis. To investigate the role of ADAP in a T cell-driven autoimmune response, we generated ADAPdeficient, BDC2.5 TCR transgenic, diabetes-prone (C57BL/6) mice (BDC/B6). We observed a striking enhancement of diabetes incidence in ADAP-deficient mice, both in animals homozygous for I-A g7 , and in mice carrying one I-A b allele (BDC/B6 g7/b ). Increased disease correlates with significantly reduced numbers of pathological CD4 + T cells in the mice. Consistent with a state of functional lymphopenia in ADAP-deficient BDC/B6 g7/b mice, T cells display increased homeostatic proliferation. Transfer of syngeneic lymphocytes or T cells both blocks ADAP-dependent diabetes and relieves exaggerated homeostatic T cell proliferation observed in ADAP-deficient mice. Marked attenuation in cellularity of the CD4 + single-positive thymocyte compartment in ADAP-deficient BDC/B6 g7/b animals suggests a mechanism for induction of the lymphopenia. We conclude that inefficient positive selection in ADAP deficiency results in lymphopenia that leads to enhanced autoimmune diabetes in the BDC/B6 g7/b model. Our findings support the notion that ineffective thymic T cell output can be a powerful causative factor in lymphopenia-driven autoimmune diabetes.