Regional distribution of calcium currents in frog semicircular canal hair cells

In the present work we studied the regional expression of voltage-dependent Ca channels in hair cells from the frog semicircular canals, employing who le-cell patch-clamp on isolated and in situ hair cells. Although Ca channel s are thought to play a major role in afferent transmission, up to now no d ata were available regarding their distribution in vestibular organs. The p roblem appears of interest, especially in the light of recent results showi ng the presence of multiple Ca current components in semicircular canal hai r cells. Our data suggest the presence, in all regions of the crista ampull aris, of two classes of cells, one displaying an inactivating Ca current (R I) and one lacking it. In the former cells, Ca current amplitude decreased from the central to the peripheral zone (the maximal currents being observe d in the intermediate zone). Only L-type and R2 current components displaye d regional differences in expression, whereas the size and properties of R1 , although variable among cells, were not regionalized. However, in cells l acking RI, Ca current amplitudes were similar regardless of cell shape and location. The possible contributions of this Ca current distribution to aff erent discharge properties are discussed. (C) 2001 Elsevier Science B.V. Al l rights reserved.