CONTROL OF NEURONAL CALCIUM CURRENT BY INTRACELLULAR CALCIUM

Rapid increases in intracellular Ca2+, created by flash photolysis of DM-nitrophen, block about half of the Ca current in internally dialyzed neurons of the snail Lymnaea stagnalis. The block is rapid and appears to be maximal by 10 ms following the flash. Ca current recovers from the block with a time constant of tens of seconds. Measurements with Ca-sensitive microelectrodes in droplets and neurons indicate that the concentration of Ca2+ does not rise above 3-mu-M following exposure to the UV flashes. These results show that intracellular Ca2+ blocks Ca channels by a relatively direct mechanism.