Voltage-independent barium-permeable channel activated in Lymnaea neurons by internal perfusion or patch excision.
Isolated nerve cells from Lymnaea stagnalis were studied using the internal-perfusion and patch-clamp techniques. Patch excision frequently activated a voltage-independent Ba2+-permeable channel with a slope conductance of 27 pS at negative potentials (50 mM Ba2+). This channel is not seen in patches on healthy cells and, unlike the voltage-dependent Ca channel, is not labile in isolated patches. The activity of the channel in inside-out patches is unaffected by intracellular ATP, Ca2+ below 1 mM or the catalytic subunit of cAMP-dependent protein kinase but is reversibly blocked by millimolar intracellular Ca2+ or Ba2+. The channel can be activated in on-cell patches by either internal perfusion with high Ca2+ or the long-term internal perfusion of low Ca2+ solutions not containing ATP. These channels may carry the inward Ca2+ current which causes a regenerative increase in intracellular Ca+ when snail neurons are perfused with high Ca2+ solutions. High internal Ca2+, or long periods of internal perfusion with ATP-free solutions, induces an increase in a resting (-50 mV) whole-cell Ba2+ conductance. This conductance can be turned off by returning the intracellular perfusate to a low Ca2+ solution containing ATP and Mg2+. The activity of this channel appears to have an opposite dependence on intracellular conditions to that of the voltage-dependent Ca channel.
Yazejian
B
B
Department of Biological Sciences, University of Southern California, Los Angeles 90089-0371.
Byerly
L
L
D000818:Animals; D001464:Barium / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D004553:Electric Conductivity; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism*; D008195:Lymnaea; D008274:Magnesium / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D010477:Perfusion
D015220:Calcium Channels; D007473:Ion Channels; D001464:Barium; D008274:Magnesium; D002118:Calcium