Nature and expression of dihydropyridine-sensitive and -insensitive calcium currents in hair cells of frog semicircular canals.
Ca(2+) currents in hair cells of the frog crista ampullaris were studied using the whole-cell patch-clamp technique. Currents were recorded in situ from hair cells in peripheral, intermediate and central regions of the sensory epithelium. Two types of Ca(2+) currents were found: a partially inactivating current that was expressed by nearly all central cells and by about 65% of intermediate and peripheral cells, and a sustained current expressed by the remaining cell population. The mean Ca(2+) current amplitude was larger in intermediate cells than in central or peripheral cells. The two types of Ca(2+) currents were composed of two components: a large, nifedipine-sensitive (NS) current and a small, nifedipine-insensitive (NI) current. The latter was resistant to SNX-482, omega-conotoxin MVIIC and omega-agatoxin IVA and to omega-conotoxin GVIA, antagonists of R, P/Q and N-type Ca(2+) channels. The amplitude of NS and NI currents varied among peripheral cells, where the current density gradually increased from the beginning of the region toward its end. No significant variation of Ca(2+) current density was detected in hair cells of either intermediate or central regions. These results demonstrate the presence of regional and intraregional variations in the expression of L and non-L Ca(2+) channels in the frog crista ampullaris. Finally, immunocytochemical investigations revealed the presence of Ca(2+) channel subunits of the alpha(1D) type and the unexpected expression of alpha(1B)-subunits.
Russo
Giancarlo
G
Dipartimento di Scienze Fisiologiche Farmacologiche Cellulari-Molecolari, Università di Pavia, Via Forlanini 6, 27100, Pavia, Italy.
Lelli
Andrea
A
Gioglio
Luciana
L
Prigioni
Ivo
I
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000096:biosynthesis* / Q000235:genetics; D004095:Dihydropyridines / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D006198:Hair Cells, Auditory / Q000187:drug effects* / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D011893:Rana esculenta; D012665:Semicircular Canals / Q000187:drug effects* / Q000378:metabolism
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004095:Dihydropyridines; C038806:1,4-dihydropyridine