Effect of a phospholipase A2 with cardiotoxin-like properties, from Bungarus fasciatus snake venom, on calcium-modulated potassium currents.
The action of a 16,300 mol. wt phospholipase A2 with cardiotoxin-like properties from Bungarus fasciatus venom on membrane electrical properties of two human cell types was examined in vitro by using tight-seal whole-cell recording methods. Epithelial cells exhibited a voltage- and Ca2(+)-activated K+ current; the sensitivity for voltage activation of the K+ current was enhanced by increasing free Ca2+ in the recording pipette from 10(-8) M to 2 x 10(-6) M. In contrast, peripheral blood lymphocytes possessed voltage-activated K+ currents that were inhibited by increasing intracellular Ca2+. Exposure of either preparation to B. fasciatus toxin (0.2-5 x 10(-6) M) for up to 30 min in the bath did not alter membrane leakage current, as judged by the maintenance of low pre-treatment values over the range of -140 mV to -40 mV. However, the sensitivity for voltage activation of the K+ current was enhanced in the epithelial cells even at the lowest concentrations tested. In contrast to the results with epithelial cells, toxin exposure inhibited the activation of voltage-activated K- currents in human lymphocytes, suggesting a specific increase in intracellular Ca2- levels in both cell types. The fluorescent probe indo-1/AM was used to monitor cytoplasmic Ca2+ levels. Exposure of either lymphocytes or epithelial cells to toxin (10(-6) M) resulted in a transient increase in Ca2+. However, while the Ca2+ response to toxin was transient, K-channel modulation by the toxin appeared to be irreversible over the experimental time course. The longer-lasting modulation of Ca2(+)-regulated K+ channels may reflect an irreversible action of the B. fasciatus phospholipase A2 on a Ca2+-dependent regulatory process.
Gong
Q H
QH
Department of Anatomy, Hahnemann University, Philadelphia, PA 19102.
Wieland
S J
SJ
Fletcher
J E
JE
Conner
G E
GE
Jiang
M S
MS
D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D004179:Cobra Cardiotoxin Proteins / Q000494:pharmacology; D004546:Elapid Venoms / Q000494:pharmacology*; D004847:Epithelial Cells; D004848:Epithelium / Q000187:drug effects; D006801:Humans; D008214:Lymphocytes / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D010740:Phospholipases / Q000494:pharmacology*; D010741:Phospholipases A / Q000494:pharmacology*; D054467:Phospholipases A2; D011188:Potassium / Q000502:physiology*
D004179:Cobra Cardiotoxin Proteins; D004546:Elapid Venoms; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D011188:Potassium; D002118:Calcium