Identification in Islets of Langerhans of a New Rat α₂-Adrenergic Receptor

The islets of Langerhans are richly innervated, and an inhibitory effect on insulin secretion, mediated through α₂-adrenergic receptors, appears to be an important physiological neural modulator of β-cell function. An α₂-receptor was cloned from isolated newborn rat islets using a polymerase chain reaction (PCR) approach. This receptor was shown by sequencing to be a new rat α₂-receptor very similar to the human α₂-C2 receptor. No other α₂-receptor subtype was identified in normal islets by the PCR using os-receptor primers. This was also the only α₂-receptor subtype present in the exocrine pancreas and liver. In contrast, in the β-cell line, βTC3, the α₂-C2 receptor was not detected, but the α₂-C4 and α₂-C10 receptor subtypes were detected. It is suggested that the α₂-C2 subtype may be the principal α₂-receptor mediating inhibitory autonomic nervous system activity in the gastrointestinal tract. A comparison of the rat islet, pancreas, and liver α₂-receptor sequences reported here with previously reported α₂-receptor sequences indicates that the rat islet α₂-receptor is not the rat α₂-C2 homologue previously denoted as RNG_α2, but is a new, fourth rat subtype with an even higher similarity to the human α₂-C2 receptor.