title: Activation of calcium influx by ATP and store depletion in primary cultures of renal proximal cells.
abstract: Cytoplasmic calcium changes and calcium influx evoked by adenosine triphosphate (ATP) were investigated in primary cultures of rabbit proximal convoluted tubule cells. Extracellular ATP (50 microM) induced a biphasic increase of [Ca2+]i measured with the calcium probe fura-2. In the early phase, the mobilization of intracellular pools resulted in a transient increase of [Ca2+]i from 106 +/- 11 nM (n = 36) to 1059 +/- 115% (n = 29) of the resting level within 10 s. In the presence of external calcium, [Ca2+]i then decreased within 3 min to a sustained level (398 +/- 38%, n = 8). Measurements of fura-2 quenching by external manganese revealed that this phase was the result of an increased Ca2+ uptake, blocked by lanthanum (10 microM) and verapamil (100 microM) but not by the nifedipin (25 microM). Internal calcium store depletion by ATP induced an increased calcium influx through lanthanum- and verapamil-sensitive, nifedipin-insensitive calcium channels, located on the apical membrane of the cells. As indicated by 86Rb+ efflux measurements, ATP activated a potassium efflux that was blocked by barium and Leiurus quinquestriatus hebraeus (LQH) venom (containing charybdotoxin) indicating the involvement of Ca(2+)-sensitive K+ channels. Moreover, in the presence of the LQH venom, the internal calcium stores were not replenished after being depleted by ATP. Our results indicate that an ATP-evoked hyperpolarization of the plasma membrane leads to increased Ca2+ influx, which facilitates the replenishment of the internal stores.
authors.affiliation: Département de Biologie Cellulaire et Moléculaire, Centre d'Etudes de Saclay, Gif sur Yvette, France.
authors.forename: J C
authors.initials: JC
authors.lastname: Cejka
authors.forename: S
authors.initials: S
authors.lastname: Le Maout
authors.forename: M
authors.initials: M
authors.lastname: Bidet
authors.forename: M
authors.initials: M
authors.lastname: Tauc
authors.forename: P
authors.initials: P
authors.lastname: Poujeol
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000172:deficiency / Q000378:metabolism*; D016764:Cell Polarity; D002478:Cells, Cultured; D018999:Charybdotoxin; D005110:Extracellular Space / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D012604:Scorpion Venoms / Q000494:pharmacology
chemical_list: D012604:Scorpion Venoms; D018999:Charybdotoxin; D000255:Adenosine Triphosphate; D011188:Potassium; D002118:Calcium