title: Actin cytoskeleton depolymerization with clostridium spiroforme toxin enhances the secretory activity of rat melanotrophs.
abstract: 1. We measured membrane capacitance (Cm) in cultured rat melanotrophs pretreated with Clostridium spiroforme toxin (CST), which specifically depolymerizes cortical filamentous actin (F-actin). Phalloidin staining confirmed that CST treatment depolymerised the F-actin. 2. In control cells, cytosol dialysis with 1 microM Ca2+i increased Cm by 23 +/- 4 % (n = 11) relative to the resting Cm 400 s after the start of patch rupture. In CST-treated cells the increase in Cm was 32 +/- 5 % (n = 15), not significantly different from controls. The rate of Cm increase was affected transiently by CST treatment, peaking at 1 min after patch rupture. The maximal rate of Cm increase was 4.27 +/- 0.85 fF s-1 (n = 12; measured 200 s after the start of patch rupture) in controls and 8.0 +/- 1.35 fF s-1 (n = 23; measured 75 s after the start of patch rupture) in CST-treated cells (P < 0.01). 3. In control cells cytosol dialysis with 0 microM Ca2+i decreased Cm by 9 +/- 3 % (n = 7), in CST-treated cells Cm increased by 11 +/- 3 % (n = 7) relative to resting Cm 400 s after the start of cytosol dialysis. The rate of change in Cm remained constant (controls: -1 to -2 fF s-1; CST treatment: 1-2 fF s-1). 4. Transient and sustained effects of CST treatment on changes in Cm at high or low [Ca2+]i, respectively, suggest a distinct role of cytoskeleton in Ca2+-dependent and Ca2+-independent changes in Cm. Transient enhancement of the rate of Cm by CST is consistent with a barrier role of cytoskeleton in regulated exocytosis. The sustained effect of CST on Ca2+-independent changes in Cm suggests cytoskeletal involvement in endocytosis.
authors.affiliation: Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Medical School, p.p. 2211, 1001 Ljubljana, Slovenija.
authors.forename: H H
authors.initials: HH
authors.lastname: Chowdhury
authors.forename: M R
authors.initials: MR
authors.lastname: Popoff
authors.forename: R
authors.initials: R
authors.lastname: Zorec
mesh_terms: D036002:ADP Ribose Transferases; D000199:Actins / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001427:Bacterial Toxins / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism*; D004553:Electric Conductivity; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D008297:Male; D008544:Melanocytes / Q000187:drug effects / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D018408:Patch-Clamp Techniques; D010590:Phalloidine; D011108:Polymers / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000199:Actins; D001427:Bacterial Toxins; D011108:Polymers; C054948:iota toxin, Clostridium spiroforme; D010590:Phalloidine; D036002:ADP Ribose Transferases; D002118:Calcium