Abstract.
Loperamide is a widely used antidiarrheal that primarily acts at nanomolar concentrations through activation of opioid receptors in the gastrointestinal tract. At somewhat higher concentrations, loperamide blocks calmodulin activity, calcium channels, N-methyl-d-aspartate-receptor channels, and maitotoxin-elicited calcium influx. Loperamide at micromolar concentrations has now been shown to have a remarkable stimulatory effect on the capacitative calcium influx that is triggered in many cells by depletion of the inositol-trisphosphate-sensitive stores of calcium in the endoplasmic reticulum. The mechanism whereby loperamide enhances levels of intracellular calcium elevated by capacitative calcium influx is, as yet, undefined.
Keywords: Key words. Loperamide; calcium channels; calcium stores; maitotoxin; inositol trisphosphate; thapsigargin; ATP.
Footnotes
Received 22 July 1999; received after revision 17 September 1999; accepted 5 October 1999