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Sauvagine Regulates Ca 2+ Oscillations and Electrical Membrane Activity of Melanotrope Cells of Xenopus laevis
Author(s) -
Cornelisse L. N.,
Deumens R.,
Coenen J. J. A.,
Roubos E. W.,
Gielen C. C. A. M.,
Ypey D. L.,
Jenks B. G.,
Scheenen W. J. J. M.
Publication year - 2002
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1046/j.1365-2826.2002.00838.x
Subject(s) - secretagogue , xenopus , medicine , endocrinology , biology , intracellular , voltage clamp , biophysics , bursting , membrane potential , patch clamp , electrophysiology , microbiology and biotechnology , secretion , biochemistry , neuroscience , gene
Ca 2+ oscillations regulate secretion of the hormone alpha‐melanphore‐stimulating hormone (α‐MSH) by the neuroendocrine pituitary melanotrope cells of the amphibian Xenopus laevis . These Ca 2+ oscillations are built up by discrete increments in the intracellular Ca 2+ concentration, the Ca 2+ steps, which are generated by electrical membrane bursting firing activity. It has been demonstrated that the patterns of Ca 2+ oscillations and kinetics of the Ca 2+ steps can be modulated by changing the degree of intracellular Ca 2+ buffering. We hypothesized that neurotransmitters known to regulate α‐MSH secretion also modulate the pattern of Ca 2+ oscillations and related electrical membrane activity. In this study, we tested this hypothesis for the secretagogue sauvagine. Using high temporal‐resolution Ca 2+ imaging, we show that sauvagine modulated the pattern of Ca 2+ signalling by increasing the frequency of Ca 2+ oscillations and inducing a broadening of the oscillations through its effect on various Ca 2+ step parameters. Second, we demonstrate that sauvagine caused a small but significant decrease in K + currents measured in the whole‐cell voltage‐clamp, whereas Ca 2+ currents remained unchanged. Third, in the cell‐attached patch‐clamp mode, a stimulatory effect of sauvagine on action current firing was observed. Moreover, sauvagine changed the shape of individual action currents. These results support the hypothesis that the secretagogue sauvagine stimulates the frequency of Ca 2+ oscillations in Xenopus melanotropes by altering Ca 2+ step parameters, an action that likely is evoked by an inhibition of K + currents.