Previous studies have shown that some of the processes related to development of sustained arrhythmias are regulated by extracellular calcium (Ca²⁺_e). This regulation by Ca²⁺_e-level is independent of the Ca²⁺-channels. In various tissues Ca²⁺_e exerts direct action on cell differentiation, cell migration, hormone secretion etc. via Ca²⁺_e-sensing receptors (CaSR). We investigated the possibility of expression of CaSR in the human heart.

The presence of CaSR mRNA in left atrial tissue was confirmed via reverse-transcription (RT)-PCR as well as with single cell RT-PCR. The CaSR protein was detected in Western blot as a specific band with the apparent size of 150–160 kD as well as by immunohistochemistry. Strong positive staining for CaSR was found in cardiomyocytes, weak staining in non-myocytes and endothelial cells and no staining in fat cells. The function of CaSR was investigated by stimulation of atrial tissue with 4 mmol ^. l^-1 Ca²⁺_e and subsequent examination of its downstream signaling pathway.

We demonstrate for the first time the presence and function of CaSR in the human atria.