Living cells interact with each other for their proper functioning. Cell signalling plays an important cell to cell interaction. Blood cells are very important as these deliver oxygen, nutrients, etc. Blood cells also interact with each other and also with the muscle cells such as endothelial cells and smooth muscle cells (the cells of blood vessel wall).
The interaction between blood cells and muscle cells is made possible with the help of special molecule found in blood known as hemoglobin. Hemoglobin carries oxygen to the muscle cells. Oxygen attaches to the hemoglobin molecule and travels through the capillaries. Oxygen is then transferred to the muscle cells when needed.