title: ATP modulation of L-type calcium channel currents in guinea pig outer hair cells.
abstract: Ca2+ channel currents and their modulation by adenosine 5'-triphosphate (ATP) in acutely isolated guinea pig outer hair cells (OHCs) were investigated using the whole-cell patch-clamp technique. The current-voltage (I-V) relation of OHCs indicated that the Ca2+ channel opened near -30 mV, and the current reached a maximum at +10 and 0 mV in 20 mM Ca2+ and Ba2+ external solutions, respectively. BayK 8644 (BayK, 2 microM) caused a 3.5-fold increase in peak Ca2+ currents and shifted the I-V curves toward more negative potentials. These results suggest that the majority of Ca2+ channels in OHCs have L-type characteristics. The effects of ATP on Ca2+ channels of OHCs were heterogenous. ATP (100 microM) decreased Ca2+ channel currents by 31.7 +/- 5.6% at 0 mV and shifted Ca2+ tail activation curves toward more depolarized potentials in some cells (N = 6). By contrast, in others, ATP enhanced the currents by 43.5 +/- 12.5% at +10 mV (N = 6). In the presence of BayK, however, ATP-induced inhibition or enhancement of Ca2+ channel currents was attenuated. In addition, 100 microM ATP produced little effect on Ca2+ channel currents in another subpopulation of cells (N = 12). This heterogenous neuromodulation of Ca2+ channel currents by ATP may reflect a functional diversity among OHCs.
authors.affiliation: Kresge Hearing Research Laboratory of the South, Department of Otorhinolaryngology and Biocommunication, Louisiana State University Medical Center, New Orleans 70112-2234, USA.
authors.forename: C
authors.initials: C
authors.lastname: Chen
authors.forename: A
authors.initials: A
authors.lastname: Nenov
authors.forename: C H
authors.initials: CH
authors.lastname: Norris
authors.forename: R P
authors.initials: RP
authors.lastname: Bobbin
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology* / Q000502:physiology; D000818:Animals; D002120:Calcium Channel Agonists / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D006168:Guinea Pigs; D018072:Hair Cells, Auditory, Outer / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D009925:Organ of Corti / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques
chemical_list: D002120:Calcium Channel Agonists; D015220:Calcium Channels; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D000255:Adenosine Triphosphate