EFFECT OF PENTACHLOROPHENOL ON CALCIUM ACCUMULATION IN BARNACLE MUSCLE-CELLS

1. The effect of extracellularly applied pentachlorophenol (PCP) was s tudied on the membrane potential (V-m) and Ca2+ uptake in isolated sin gle skeletal muscle cells of Balanus nubilus. 2. When compared with th e controls, 0.1 mM PCP induced a significant (P < 0.05) increase in Ca 2+ uptake accompanied by membrane depolarization (9 mV at 45 min incub ation). This depolarization was reduced by 11% if extracellular Ca2+ ( Ca-o(2+)) was replaced by Tris(+) and by 50% if extracellular Na+ was also replaced by Tris(+). 3.The Ca2+ channel blocker, verapamil (0.1 m M), completely inhibited the PCP-induced Ca2+ uptake as well as the me mbrane depolarization either in the absence or presence of Ca-o(2+). E xperiments on voltage-clamped cells show that the PCP-induced Ca2+ upt ake was independent of the PCP-induced depolarization. 4. The results indicate that PCP induces activation of a verapamil-sensitive Ca2+ inf lux pathway (presumably L-type Ca2+ channels) independent of V-m. The permeation of Ca2+, Na+ and Tris(+) through this pathway produces memb rane depolarization in the following order of effectiveness: Ca2+ > Na + > Tris(+).