Ca2resepsjon

Ca2resepsjon refers to the cellular processes by which cells detect extracellular calcium ions (Ca2+) and convert the signal into intracellular responses. Calcium acts as a universal second messenger in many tissues, and reception involves specialized receptors and channels, notably the calcium-sensing receptor (CaSR) and various calcium-permeable channels.

The calcium-sensing receptor (CaSR) is a class C G-protein-coupled receptor located on the surface of parathyroid cells, kidney tubules, and other tissues. It senses extracellular Ca2+ concentrations and modulates signaling pathways via G proteins, leading to changes such as phospholipase C activation, inositol trisphosphate production, calcium release from internal stores, and adjustments in parathyroid hormone secretion and renal calcium handling.

In addition to CaSR, Ca2+ entry and release involve voltage-gated calcium channels, ligand-gated channels, and intracellular release from the endoplasmic reticulum through IP3 receptors and ryanodine receptors. Intracellular Ca2+ is buffered by proteins such as calmodulin, and plasma membrane pumps and exchangers help restore resting levels after signaling events.

Ca2resepsjon regulates a wide range of physiological processes, including neuronal transmission and plasticity, muscle contraction, hormone secretion, blood coagulation, enzyme activity, and gene expression. Its activity is tightly controlled by hormonal systems such as parathyroid hormone, calcitonin, and vitamin D, which maintain plasma Ca2+ within a narrow range.

Clinically, dysregulation of Ca2+ reception can lead to hypercalcemia or hypocalcemia. Mutations in CaSR can cause familial hypocalciuric hypercalcemia or neonatal severe hyperparathyroidism. Therapies targeting CaSR, such as calcimimetics (e.g., cinacalcet), illustrate the medical relevance of Ca2resepsjon.