Ca extrusion via putative Na:Ca or Na:Ca,K exchanger was investigated in hair cells isolated from frog semicircular canals. Reverse exchange was probed in patch-clamped cells, dialyzed with a Ca-, K-free solution containing 115 Na (concentrations in mM), upon switching from Ca-free, 115 Li extemal solution to 4 Ca+115 Li or to 4 Ca+20 K+95 Li solution. The voltage-dependent K and Ca currents were blocked with extemal 15 TEA, 5 Cs and 0.2 Cd; the holding potential was -70 mV. After correcting for the leak change upon switching from the extemal Ca-free solution to 4 Ca, no actual current changes were evoked by the solutions tested. In lizard rod photoreceptors in the same condìtions, peak exchange currents exceeding 100 pA were recorded in the Ca+ K extemal solution. The forward exchange mode was probed by rapidly increasing the intracellular Ca concentration by means of flash photolysis of two novel caged Ca complexes of 4-(2 nitrophenyl)-3,6-dioxaoctanedioic acid and 4-(4,5-dimethoxy-2- nitrophenyl)-3,6-dioxaoctanedioic acid in the presence of internal K and extemal Na. No currents were evoked by the Ca jump, whereas in rod photoreceptors, forward exchange currents up to 50 pA were recorded in the same conditions. It was concluded that neither Na:Ca nor Na:Ca,K electrogenic exchanger exists in this hair celi type.
NEITHER Na:Ca NOR Na:Ca,K ELECTROGENIC EXCHANGER EXISTS IN FROG SEMICIRCULAR CANAL HAIR CELLS
MARTINI, Marta;ROSSI, Marialisa;FARINELLI, Federica;RISPOLI, Giorgio
2002
Abstract
Ca extrusion via putative Na:Ca or Na:Ca,K exchanger was investigated in hair cells isolated from frog semicircular canals. Reverse exchange was probed in patch-clamped cells, dialyzed with a Ca-, K-free solution containing 115 Na (concentrations in mM), upon switching from Ca-free, 115 Li extemal solution to 4 Ca+115 Li or to 4 Ca+20 K+95 Li solution. The voltage-dependent K and Ca currents were blocked with extemal 15 TEA, 5 Cs and 0.2 Cd; the holding potential was -70 mV. After correcting for the leak change upon switching from the extemal Ca-free solution to 4 Ca, no actual current changes were evoked by the solutions tested. In lizard rod photoreceptors in the same condìtions, peak exchange currents exceeding 100 pA were recorded in the Ca+ K extemal solution. The forward exchange mode was probed by rapidly increasing the intracellular Ca concentration by means of flash photolysis of two novel caged Ca complexes of 4-(2 nitrophenyl)-3,6-dioxaoctanedioic acid and 4-(4,5-dimethoxy-2- nitrophenyl)-3,6-dioxaoctanedioic acid in the presence of internal K and extemal Na. No currents were evoked by the Ca jump, whereas in rod photoreceptors, forward exchange currents up to 50 pA were recorded in the same conditions. It was concluded that neither Na:Ca nor Na:Ca,K electrogenic exchanger exists in this hair celi type.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
