Osteocytes maintain matrix mineral levels by secreting:

1. Osteocytes are sealed in lacunae. 2. They still regulate the surrounding matrix. 3. Osteocytes maintain the mineral concentration of the matrix via the secretion of enzymes. 4. So the answer is enzymes. _Source: OpenStax 'Anatomy and Physiology 2e', Ch 6 'Bone Tissue and the Skeletal System'_