Pancreatic α-cells exhibit oscillations in cytosolic Ca²⁺(Ca²⁺_c), which control pulsatile glucagon (GCG) secretion. However, the mechanisms that modulate α-cell Ca²⁺_coscillations have not been elucidated. As β-cell Ca²⁺_coscillations are regulated in part by Ca²⁺-activated K⁺(K_slow) currents, this work investigated the role of K_slowin α-cell Ca²⁺handling and GCG secretion. α-Cells displayed K_slowcurrents 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 K_slowwas 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 K_slowwith apamin depolarized membrane potential ( V_m) (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⁺_cwas 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⁺_cfollowing prolonged K_slowinhibition, apamin decreased GCG secretion from mouse (20.4 ± 4.2%) and human (27.7 ± 13.1%) islets at low glucose. These data demonstrate that K_slowactivation provides a hyperpolarizing influence on α-cell V_mthat sustains Ca²⁺entry during hypoglycemic conditions, presumably by preventing voltage-dependent inactivation of P/Q-type VDCCs. Thus, when α-cell Ca²⁺_cis elevated during secretagogue stimulation, K_slowactivation helps to preserve GCG secretion.