Voltage- and Ca2+-dependent, slow-activating vacuolar (SV) channels represent the major cation conductance of the plant vacuole membrane and have been implicated in calcium-induced calcium release (CICR) from intracellular stores. Encoded by the TWO PORE CHANNEL 1 gene, the Arabidopsis thaliana SV channel AtTPC1 has become a paradigm in understanding the synergistic action of membrane potential and cytosolic Ca2+ transients for channel gating. Novel AtTPC1 structural data give rise to emerging models describing the intermediate conformational transitions during channel opening and the resulting functional consequences. Across phyla, voltage-gated ion channels (VGICs) allow excitability. The vacuolar two-pore channel AtTPC1 from the tiny mustard plant Arabidopsis thaliana has emerged as a paradigm for deciphering the role of voltage and calcium signals in membrane excitation. Among the numerous experimentally determined structures of VGICs, AtTPC1 was the first to be revealed in a closed and resting state, fueling speculation about structural rearrangements during channel activation. Two independent reports on the structure of a partially opened AtTPC1 channel protein have led to working models that offer promising insights into the molecular switches associated with the gating process. We review new structure–function models and also discuss the evolutionary impact of two-pore channels (TPCs) on K+ homeostasis and vacuolar excitability. [ABSTRACT FROM AUTHOR]