Alpha-latrotoxin stimulates inward current, rise in cytosolic calcium concentration, and exocytosis in at pituitary gonadotropes.
Alpha-latrotoxin (LTX) from the black widow spider venom, stimulates neurotransmitter release from neuronal cells via Ca2+ -dependent as well as Ca2+ -independent mechanisms. In some peptide-secreting endocrine cells, however, LTX stimulates hormone release mainly via a Ca2+ -independent mechanism. Here we investigated the action of LTX in rat pituitary gonadotropes that secrete the peptide, LH. Using the patch-clamp technique in conjunction with the fluorescent Ca2+ indicator (indo-1) to simultaneously measure the cytosolic Ca2+ concentration ([Ca2+]i) and ionic current, we showed that LTX elicited bursts of inward current that were accompanied by [Ca2+]i elevations. In the presence of a physiological concentration of extracellular Ca2+, the unitary conductance of the LTX-induced current was about 300 pS, and only about 6.4% of the current was carried by Ca2+. The LTX-induced current was occasionally followed by intracellular Ca2+ release. At [Ca2+]i of 1 microM or more, exocytosis (detected by membrane capacitance measurement) was consistently triggered, and it was frequently followed by endocytosis. Thus, LTX triggers Ca2+ -dependent exocytosis in gonadotropes via extracellular Ca2+ entry as well as intracellular Ca2+ release. In approximately 25% of the cells, LTX could also trigger a slow exocytosis in the absence of [Ca2+]i elevation. Therefore, LTX has both Ca2+ -dependent and Ca2+ -independent actions in gonadotropes.
Tse
F W
FW
Department of Pharmacology, University of Alberta, Edmonton, Canada.
Tse
A
A
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002412:Cations / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism*; D004553:Electric Conductivity; D005089:Exocytosis / Q000187:drug effects*; D005110:Extracellular Space / Q000378:metabolism; D006065:Gonadotropins, Pituitary / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism; D008297:Male; D009994:Osmolar Concentration; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013111:Spider Venoms / Q000494:pharmacology*
D002412:Cations; D006065:Gonadotropins, Pituitary; D007473:Ion Channels; D013111:Spider Venoms; C020763:alpha-latrotoxin; D002118:Calcium