Intracellular Ca²⁺ ([Ca²⁺]_i) can rise primarily via release from intracellular storage sites (e.g., the endoplasmic reticulum) or via entry across the membrane down the steep concentration gradient (1–3). Ca²⁺ can enter through two main classes of plasma membrane-located Ca²⁺ channels: receptor operated and voltage sensitive (4–7). Voltage-sensitive Ca²⁺ channels are involved in a wide and diverse array of physiological responses including neurotransmitter release (8). In addition, many guanine nucleotide protein (G) coupled receptors couple to voltage-sensitive Ca²⁺ channels to reduce Ca²⁺ influx (9,10).