Effects of verapamil on down-regulation of norepinephrine-induced beta adrenoceptors in cultured rat cardiomyocytes.

AIM: To determine whether verapamil (Ver) inhibits norepinephrine (NE)-induced beta adrenoceptors down-regulation in cultured rat cardiomyocytes. METHODS: [3H]-Dihydroalprenolol (DHA) radiobinding assay was used to measure beta adrenoceptor density, fluorescent indicator Fura 2-AM was used to estimate levels of free cytosolic calcium ([Ca2+]i). RESULTS: Ver reduced [Ca2+]i and increased beta adrenoceptor density, NE increased [Ca2+]i and reduced beta adrenoceptor density of cultured cardiomyocytes, these effects were time and concentration dependent. Ver inhibited the above effects of NE. CONCLUSIONS: Ver increased beta adrenoceptor density and inhibited NE-induced beta adrenoceptor down-regulation of cardiomyocytes.