We investigated the possibilìty that, in hair cells mechanically isolated from frog semicircular canals, Ca extrusion occurs via a Na:Ca (cardiac type) or Na:Ca,K (retinal type) exchanger. Cells concurrentiy imaged during whole-cell patch-clamp recordings using the Ca sensitive fluorescent dye Oregon Green 488 BAPTA-1 (100 microM) showed no voltage dependence of Ca clearance dynamics foliowing a Ca Ioad through voltage-gated Ca channels. Reverse exchange was probed in hair cells dialyzed with a Ca- and K-free solution, containing a saturating Na concentration, after zeroing the contribution to the whole-celi current from Ca and K conductances. In these conditions, no reverse exchange current was detected upon switching from a Ca-free external solution to a solution containing saturating concentrations of Ca alone or Ca+K. By contrast, the same experimental protocol elicited peak exchange currents exceeding 100 pA in vertebrate rod photoreceptors, used as positive controls. In both cell types, we also probed the forward exchange mode by rapidly increasing the intracellular Ca concentration using flash photolysis of two novel caged Ca complexes, 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 external Na. No currents were evoked by UV-triggered Ca jumps in hair cells, whereas exchanger conforrnational currents up to 400 pA, foliowed by saturating forward exchange currents up to 30 pA, were recorded in rod photoreceptors subjected to the same experimental conditions. We conclude that neither Na:Ca nor Na:Ca,K electrogenic exchanger exists in this hair cell type.
NO EVIDENCE FOR RETINAL OR CARDIAC TYPE EXCHANGER IN FROG SEMICIRCULAR CANAL HAIR CELLS
MARTINI, Marta;ROSSI, Marialisa;FARINELLI, Federica;RISPOLI, Giorgio
2002
Abstract
We investigated the possibilìty that, in hair cells mechanically isolated from frog semicircular canals, Ca extrusion occurs via a Na:Ca (cardiac type) or Na:Ca,K (retinal type) exchanger. Cells concurrentiy imaged during whole-cell patch-clamp recordings using the Ca sensitive fluorescent dye Oregon Green 488 BAPTA-1 (100 microM) showed no voltage dependence of Ca clearance dynamics foliowing a Ca Ioad through voltage-gated Ca channels. Reverse exchange was probed in hair cells dialyzed with a Ca- and K-free solution, containing a saturating Na concentration, after zeroing the contribution to the whole-celi current from Ca and K conductances. In these conditions, no reverse exchange current was detected upon switching from a Ca-free external solution to a solution containing saturating concentrations of Ca alone or Ca+K. By contrast, the same experimental protocol elicited peak exchange currents exceeding 100 pA in vertebrate rod photoreceptors, used as positive controls. In both cell types, we also probed the forward exchange mode by rapidly increasing the intracellular Ca concentration using flash photolysis of two novel caged Ca complexes, 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 external Na. No currents were evoked by UV-triggered Ca jumps in hair cells, whereas exchanger conforrnational currents up to 400 pA, foliowed by saturating forward exchange currents up to 30 pA, were recorded in rod photoreceptors subjected to the same experimental conditions. We conclude that neither Na:Ca nor Na:Ca,K electrogenic exchanger exists in this hair cell type.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
