Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1974311 | Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology | 2006 | 13 Pages |
The aim of the present study was to assess the cellular mechanism of secretion in the salivary gland of the snail, Helix pomatia, using electrophysiological, electron microscopic and immunohistochemical techniques. A homogeneously distributed membrane potential (− 56.6 ± 9.8 mV) was determined mainly by a K+-electrochemical gradient and partly by the contribution of the electrogenic Na+-pump and Cl− conductance. Low resistance electrical coupling sites were identified physiologically. Transmission electron microscopy and innexin 2 antibody revealed the presence of gap–junction-like membrane structures between gland cells. It is suggested that gap–junctions are sites of electrotonic intercellular communication, which integrate the gland cells into a synchronized functional unit in the acinus. Stimulation of the salivary nerve elicited secretory potentials (depolarization) which could be mimicked by local application of acetylcholine, dopamine or serotonin. In voltage-clamp experiments four major conductances were identified: a delayed rectifier (IK), a transient (IA) and a Ca2+-activated outward K+ current (IK(Ca)) and Ca2+-inward currents (ICa). It is suggested that one or more of these conductances may give rise to a stimulus activated secretory potential leading to excitation–secretion coupling and subsequent the release of the mucus from the gland cells.