Voltage Dependence and pH Regulation of Human Polycystin-2-mediated Cation Channel Activity

SILVIA GONZALEZ-PERRETT, MARISA BATELLI, KEETAE KIM, MAKRAM ESSAFI, GUSTAVO TIMPANARO, NICOLAS MONTALBETTI, IGNACIO L. REISIN, M. AMIN ARNAOUT, AND HORACIO F. CANTIELLO

JOURNAL OF BIOLOGICAL CHEMISTRY

Año: 2002 p. 24959 - 24966

0021-9258

Polycystin-2, the product of the human PKD2 gene, whose mutations cause autosomal dominant polycystic kidney disease, is a large conductance, Ca2-permeable non-selective cation channel. Polycystin-2 is functionally expressed in the apical membrane of the human syncytiotrophoblast, where it may play a role in the control of fetal electrolyte homeostasis. Little is known, however, about the mechanisms that regulate polycystin- 2 channel function. In this study, the role of pH in the regulation of polycystin-2 was assessed by ion channel reconstitution of both apical membranes of human syncytiotrophoblast and the purified FLAG-tagged protein from in vitro transcribed/translated material. A kinetic analysis of single channel currents, including dwell time histograms, confirmed two open and two close states for spontaneous channel behavior and a strong voltage dependence of the open probability of the channel (Po). A reduction of cis pH (pHcis) decreased Po and shifted the voltage dependence of channel function but had no effect on the single channel conductance. An increase in pHcis, in contrast, increased NPo (channel number times Po). Elimination of the H chemical gradient did not reverse the low pHcis inhibition of polycystin-2. Similar findings confirmed the pH effect on the in vitro translated, FLAG-tagged purified polycystin-2. The data indicate the presence of an H ion regulatory site in the channel protein, which is accessible from the cytoplasmic side of the protein. This protonation site controls polycystin-2 cation-selective channel activity.PKD2 gene, whose mutations cause autosomal dominant polycystic kidney disease, is a large conductance, Ca2-permeable non-selective cation channel. Polycystin-2 is functionally expressed in the apical membrane of the human syncytiotrophoblast, where it may play a role in the control of fetal electrolyte homeostasis. Little is known, however, about the mechanisms that regulate polycystin- 2 channel function. In this study, the role of pH in the regulation of polycystin-2 was assessed by ion channel reconstitution of both apical membranes of human syncytiotrophoblast and the purified FLAG-tagged protein from in vitro transcribed/translated material. A kinetic analysis of single channel currents, including dwell time histograms, confirmed two open and two close states for spontaneous channel behavior and a strong voltage dependence of the open probability of the channel (Po). A reduction of cis pH (pHcis) decreased Po and shifted the voltage dependence of channel function but had no effect on the single channel conductance. An increase in pHcis, in contrast, increased NPo (channel number times Po). Elimination of the H chemical gradient did not reverse the low pHcis inhibition of polycystin-2. Similar findings confirmed the pH effect on the in vitro translated, FLAG-tagged purified polycystin-2. The data indicate the presence of an H ion regulatory site in the channel protein, which is accessible from the cytoplasmic side of the protein. This protonation site controls polycystin-2 cation-selective channel activity.