How can cytosolic Ca²⁺ concentrations be increased?

Cytosolic Ca²⁺ concentrations can be increased by opening voltage-gated Ca²⁺ channels. When these channels open, they allow calcium ions, which are often in higher concentrations outside the cell compared to the inside, to flow into the cytoplasm. This influx of calcium is a crucial signaling mechanism in various physiological processes, including muscle contraction, neurotransmitter release, and cell signaling pathways.

Voltage-gated Ca²⁺ channels are particularly important in excitable tissues, such as neurons and muscle cells, where their opening is triggered by depolarization of the membrane. This rapid increase in intracellular calcium not only contributes to immediate cellular responses but also plays a role in long-term cellular changes by activating various signaling pathways.

Other choices would not lead to an increase in cytosolic Ca²⁺ levels. For instance, phosphorylating proteins or inhibiting protein kinases does not directly increase Ca²⁺ concentrations, but rather may modulate other cellular pathways. Closing voltage-gated Ca²⁺ channels effectively reduces calcium entry into the cell, leading to lower cytosolic Ca²⁺ levels.