title: Caribbean maitotoxin elevates [Ca(2+)]i and activates non-selective cation channels in HIT-T15 cells.
abstract: OBJECTIVE
  To investigate the cytotoxic mechanism of caribbean maitotoxin (MTX-C) in mammalian cells.
  
  
  METHODS
  We used whole-cell patch-clamp techniques and fluorescence calcium imaging to determine the cellular toxic mechanisms of MTX-C in insulin secreting HIT-T15 cells, which is a system where the effects of MTX have been observed. HIT-T15 cells stably express L-type calcium current, making it a suitable model for this study. Using the fluorescence calcium indicator Indo-1 AM, we found that there is a profound increase in HIT-T15 intracellular free calcium 3 min after application of 200 nmol/L MTX-C.
  
  
  RESULTS
  About 3 min after perfusion of MTX-C, a gradual increase in free calcium concentration was observed. This elevation was sustained throughout the entire recording period. Application of MTX-C did not elicit the L-type calcium current, but large cationic currents appeared after applying MTX-C to the extracellular solution. The current-voltage relationship of the cation current is approximately linear within the voltage range from -60 to 50 mV, but flattened at voltages at -80 and -100 mV. These results indicate that MTX-C induces a non-voltage activated, inward current under normal physiological conditions, which by itself or through a secondary mechanism results in a large amount of cationic influx. The biophysical mechanism of MTX-C is different to its isoform, pacific maitotoxin (MTX-P), when the extracellular calcium is removed.
  
  
  CONCLUSIONS
  We conclude that MTX-C causes the opening of non-selective, non-voltage-activated ion channels, which elevates level of intracellular calcium concentration and leads to cellular toxicities.
authors.affiliation: Xin-Zhong Lu, Department of Pharmacology, University of South Alabama, Mobile, AL 36688, United States.
authors.forename: Xin-Zhong
authors.initials: XZ
authors.lastname: Lu
authors.forename: Robert
authors.initials: R
authors.lastname: Deckey
authors.forename: Guo-Liang
authors.initials: GL
authors.lastname: Jiao
authors.forename: Hui-Feng
authors.initials: HF
authors.lastname: Ren
authors.forename: Ming
authors.initials: M
authors.lastname: Li
keywords: Calcium fluorescence; High voltage gated Ca2+ channels; Insulin secreting cells; Maitotoxin; Whole cell patch clamp