Modulation of the human polycystin-L channel by voltage and divalent cations.
Polycystin-L (PCL) is highly homologous in sequence and membrane topology to polycystin-2, the product of the second gene responsible for autosomal dominant polycystic kidney disease (ADPKD). PCL and polycystin-2 were recently shown to be Ca2+-permeable, Ca2+-activated cation channels. Further characterization of polycystins will help in the understanding of cystogenesis and pathogenesis of ADPKD. In the present study, we expressed human PCL in Xenopus oocytes and studied its function utilizing patch-clamp and two-electrode voltage clamp techniques. In addition to its permeability to Ca2+, K+ and Na+, PCL was highly permeable to NH4+ and Cs+ with a permeability ratio NH4+:Cs+:Na+ of 2.2:1.02:1. Voltage modulation of channel properties was studied using cell-attached (C-A) and excised inside-out (I-O) patches. In the C-A mode, the open probability (NP(o)) of PCL at negative potentials (NP(o)=0.22) was higher than at positive potentials (NP(o)=0.05). The mean open time averaged 31.6 ms at negative potentials, and 6.2 ms at positive potentials; single-channel activity exhibited bursts with a mean interburst time of 178 ms. Using I-O patches under symmetrical ionic conditions, single-channel inward conductance was significantly larger than outward conductance, indicating a slight inward rectification. External Mg2+ inhibited the PCL channel currents. The inhibitory effect was voltage-dependent and substantially reduced by depolarization. The time course of inactivation depended on external calcium concentration but was independent of voltage and peak current. This study shows that although PCL is not a voltage-gated channel, its channel activity and inhibition by Mg2+ are modulated by membrane potential.
Liu
Yan
Y
Membrane Protein Research Group, Department of Physiology, University of Alberta, 729 MSB, T6G 2H7, Edmonton, AB, Canada.
Li
Qiang
Q
Tan
Miao
M
Zhang
Yu-Yang
YY
Karpinski
Edward
E
Zhou
Jing
J
Chen
Xing-Zhen
XZ
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D015220:Calcium Channels; D002413:Cations, Divalent / Q000378:metabolism / Q000494:pharmacology*; D002586:Cesium / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology*; D008562:Membrane Glycoproteins / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010750:Phosphoproteins / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D011956:Receptors, Cell Surface; D012964:Sodium / Q000378:metabolism; D014162:Transfection; D014981:Xenopus
D015220:Calcium Channels; D002413:Cations, Divalent; D008562:Membrane Glycoproteins; C117185:PKD2L1 protein, human; D010750:Phosphoproteins; D000644:Quaternary Ammonium Compounds; D011956:Receptors, Cell Surface; D002586:Cesium; D012964:Sodium; D008274:Magnesium; D011188:Potassium; D002118:Calcium