High density of beta 2-adrenoceptors in a human keratinocyte cell line with complete epidermal differentiation capacity (HaCaT)

Abstract

A non-tumorigenic keratinocyte cell line with complete epidermal differentiation capacity (HaCaT) was used in radioligand binding experiments to determine the number of beta-adrenoceptors. Intact cells were saturated with 3H-labelled (-)CGP-12177 (CGP), a hydrophilic non-selective beta-adrenergic antagonist as radioligand. In order to investigate the beta-adrenergic subtype selectivity, displacement experiments were performed with different antagonists and agonists. Binding of CGP to keratinocytes has been shown to be reversible and saturable and to have high affinity (Bmax = 114.0 +/- 8.8 fmol/10(7) cells with 6866 receptors/cell, KD = 0.095 +/- 0.017 nmol/l; n = 11). Beta-adrenergic antagonists inhibited binding yielding monophasic displacement curves. IC50-values (nmol/l) were: propranolol (non-selective) 1.68; CGP-12177 (non-selective) 1.08; ICI 118,551 (beta 2-selective) 2.92; bisoprolol (beta 1-selective) 1230; and CGP-20712 (beta 1-selective) 24,980. Agonists displaced CGP in the order isoprenaline greater than adrenaline greater than noradrenaline. We conclude that HaCaT cells express a high density of beta2-adrenoceptors providing a good model system to study adrenergic receptor mechanisms under reproducible experimental conditions in keratinocytes.