Effects of extracellular calcium on fASIC1 currents.
Fish ASIC1 (fASIC1) cloned from Opsanus tau, unlike the rat ASICs, requires Ca(2+) in the extracellular preconditioning solution (pH 7.4) to be activated. Here we show that fASIC1 is interacting with Ca(2+) in the same way as mammalian ASICs: extracellular Ca(2+) is increasing the proportion of channels available for activation by stabilizing the closed state of the channel; in the activation process Ca(2+) is released; H(+) compete for the binding site of Ca(2+) making the gating mechanism both Ca(2+) and H(+) dependent; H(+) stabilizes the desensitized state; Ca(2+) blocks the fASIC1 channel; and the affinity of the block is also modulated by H(+). The "Ca(2+) activation requirement" of fASIC1 reflects its greater affinity for steady-state desensitization by H(+) compared to mammalian ASIC1.
Todorović
Natasa
N
Institute for Biological Research Sinisa Stanković, Belgrade, Serbia and Montenegro. nara@ibiss.bg.ac.yu
Corić
Tatjana
T
Zhang
Ping
P
Canessa
Cecilia
C
D062565:Acid Sensing Ion Channels; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005110:Extracellular Space / Q000378:metabolism*; D005399:Fishes; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects* / Q000502:physiology; D008565:Membrane Proteins / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology; D011522:Protons; D051381:Rats; D015222:Sodium Channels / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology
D062565:Acid Sensing Ion Channels; C568268:Asic1 protein, rat; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D011522:Protons; D015222:Sodium Channels; D002118:Calcium