Glucagon acts mainly on

Glucagon primarily acts on liver cells (hepatocytes). Glucagon is a peptide hormone produced by the alpha cells of the pancreas. 

When blood glucose levels drop (for example, between meals or during periods of fasting), glucagon is released. Its main target is the liver, where it triggers several processes that increase blood glucose levels:

• Glycogenolysis: Glucagon stimulates the breakdown of glycogen, a storage form of glucose in the liver, into glucose. This glucose is released into the bloodstream to raise blood sugar levels.
• Gluconeogenesis: Glucagon promotes gluconeogenesis, which is the synthesis of glucose from non-carbohydrate precursors like amino acids and fats. This process also contributes to elevating blood glucose levels.
• Decreased Glycolysis: Glucagon inhibits glycolysis, the breakdown of glucose within cells. This reduces the utilization of glucose by liver cells, conserving it for release into the bloodstream.

The combined effect of these actions helps to prevent hypoglycemia (low blood sugar) and maintain a stable glucose level between meals or during fasting periods.