Heterogeneity of hair cells in the bullfrog sacculus

Morphometric and electrophysiological features of hair cells in the sacculus of the bullfrog (Rana catesbeiana) were studied. Confocal microscopy observations of hair cells in situ revealed that three classes of hair cells can be distinguished by their somata shape and macular location. Two of these, termed central cylindrical (CCHCs) and central flask-shaped (CFHCs) hair cells, were found in the central part of the macula. The third class, termed peripheral elongated hair cells (PEHC), was only found around the perimeter of the sacculus. Using the whole-cell patch-clamp technique CCHCs and CFHCs were distinguished by the amplitude of their voltage-activated calcium currents (ICa). The mean amplitudes of steady-state ICa at -20 mV were -900 +/- 500 pA (n = 18) for CCHCs and -160 +/- 70 pA (n = 10) for CFHCs. The two hair-cell types also differed in the possession of a Cs+-resistant, apamin-sensitive, calcium-sensitive potassium current, found only the CFHCs. This study indicates that several populations of hair cells with distinct morphological features exist in the bullfrog sacculus, and that at least two of these differ in their complement of membrane conductances.