Detection of endothelin receptors in rat and guinea-pig airway nerves by immunohistochemistry

We investigated the existence of endothelin (ET) receptor subtypes in airway neurones from the rat and guinea-pig and determined the ability of these receptors to modulate contractile function. Rat tracheal neuron cultures as well as rat and guinea-pig whole mount preparations were labelled with antibodies to the cholinergic nerve marker choline acetyltransferase (ChAT), the neuron specific marker protein gene product 9.5 (PGP 9.5) and to ET(A)and ET(B)receptors. Following incubation with fluorescent secondary antibodies, fluorescence was detected using confocal microscopy with dual emission protocols. Specific fluorescence was detected both in whole mount preparations and neuron cultures, in association with the primary antibodies. Specific fluorescence associated with either ET(A)and ET(B)receptors was colocalized with that for PGP 9.5. Despite the presence of ET(A)and ET(B)receptors on airway nerves, ET-1 failed to significantly alter cholinergic, excitatory or inhibitory non-adrenergic-non-cholinergic nerve-mediated responses in guinea-pig airways. This is in sharp contrast to ET-1-induced potentiation of responses to cholinergic nerve-evoked contraction in rat trachea. Thus, although ET(A)and ET(B)receptors exist in airway cholinergic neurons in whole mount preparations and in primary neuron cultures from rat and guinea-pig trachea, the influence of these receptors on contractile function appears to be species-dependent.

Immunocytochemical detection of endothelin receptors in rat cultured airway nerves

Endothelin-1 (ET-1) has been shown to potentiate cholinergic neurotransmission in human bronchus as well as in airways from a variety of animal species, suggesting that ET receptors exist prejunctionally on airway cholinergic nerves. We have successfully isolated and maintained rat tracheal para-sympathetic neurons in culture. Most cultured cells were associated with specific fluorescence for the nerve cell marker protein gene product 9.5 (PGP 9.5). These cultures contained a high proportion of parasympathetic neurons. Importantly, specific immunofluorescent antibodies for ETB receptors were colocalized with those for PGP 9.5. Therefore, for the first time, ETB receptors have been shown to exist on airway parasympathetic neurons in culture.