Figure 2. Molecular characterization of the Na⁺ channels expressed by single utricle hair cells.

A, Nomarski micrograph of a utricle hair cell. The recording electrode, of which only the tip is in focus, approaches the basolateral part of an exposed cell. Upper inset, fast time scale observation of the whole-cell current showing I_Na recorded following the protocol described in Fig. 1 (rR_s 1.3 MΩ, C_m 6.9 pF). Bottom inset, plot of current amplitudes taken either at the peak of the inward current (▪) or 5 ms after the beginning of the test pulse (○), as a function of the test potential for the hair cell shown. B, agarose gel electrophoresis of single-cell RT-PCR products obtained after the second round of amplifications using specific primers for Na⁺ channel α-subunits (Nav1.1, Nav1.2, Nav1.3, Nav1.6, Nav1.7) for the P3 cell recorded in A. Products were resolved with SmartLadder (Eurogentec) as a molecular weight marker (M). C1, expression profiles recovered from four P1–P2 cells showing a high diversity of expression profiles from cell to cell. C2, validation of the sequence identity of Nav1.1, Nav1.2, Nav1.3, Nav1.6 and Nav1.7 is demonstrated by expected restriction fragments sizes obtained by using specific restriction enzymes, Taq I, Aci I, Bsm F1, Ban II and Ava II for each of the five isoforms respectively. D, relative frequency expressed in percent of each Na⁺ α-subunit mRNA in the 13 cells analysed between P1 and P3.