There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
The activity of melanotroph cells of the amphibian pars intermedia is regulated by
multiple factors including classical neurotransmitters and neuropeptides. In this
study, we have examined the possible involvement of acetylcholine (ACh) in the regulation
of electrical and secretory activities of frog pituitary melanotrophs. Electrophysiological
recordings were conducted on cultured cells by using the patch-clamp technique in
the whole-cell configuration. In parallel, alpha-MSH release from acutely dispersed
pars intermedia cells was studied by means of the perifusion technique. In all cells
tested in the current-clamp mode, superfusion with ACh (10(-6) M) gave rise to a depolarization
associated with an enhanced frequency of action potentials. Administration of ACh
(10(-6) M) to perifused cells also induced stimulation of alpha-MSH release. These
results indicate that the neurotransmitter ACh exerts a direct stimulatory effect
on pituitary melanotrophs. The action of ACh on electrical and secretory activities
was mimicked by muscarine (10(-5) M), while ACh-induced alpha-MSH secretion was completely
abolished by the muscarinic antagonist atropine (10(-6) M). The depolarizing effect
of muscarine was suppressed by the specific M1 muscarinic antagonist pirenzepine (10(-5)
M), indicating the existence of a M1 subtype muscarinic receptor in frog pars intermedia
cells. In addition, using a monoclonal antibody against calf muscarinic receptors,
we have visualized, by the immunofluorescence technique, the presence of muscarinic
receptor-like immunoreactivity in cultured intermediate lobe cells. Electrophysiological
recordings showed that nicotine (10(-5) M) induces membrane depolarization associated
with an increase of the frequency of action potentials.(ABSTRACT TRUNCATED AT 250
WORDS)