Benzodiazepine binding sites in rat submaxillary gland: absence of markers of GABA system.

Specific binding of [3H]diazepam to the nuclear, mitochondrial and microsomal subcellular fractions of the rat submaxillary gland is reported. Apparent KD values were similar in the three fractions studied (around 80 nM). The nuclear and mitochondrial fractions contain 95% of the total sites detected (20 pmoles/mg prot.). The sites exhibit a much higher affinity for Ro 5-4864 than for clonazepam or Ro 15-1788, and are not modified by 10(-6) to 10(-4) GABA or 10(-5) M bicuculline. Neither sympathetic denervation or parasympathetic decentralization modified [3H]Dz binding, which is found to be considerably lower in the early post-natal state as well as following duct ligation of the gland of adult rats. The results suggest that these peripheral Bz binding sites are mainly located in the acini. No specific GABA binding or GAD activity was detected either in the presence or absence of NaCl. Very low levels of endogenous GABA (58 +/- 3 nmoles/g tissue) were found in homogenates of the gland.