Mechanosensitivity of mammalian auditory hair cells in vitro

Intracellular responses recorded in vitro from the cochleas of anaesthetized mammals have shown that the mechanoreceptive inner and outer hair cells are sharply tuned, accounting for many of the properties of the afferent fibres in the auditory nerve. However, in vivo it has not been possible to measure directly the excitatory mechanical input to these cells (the displacement of their mechanosensitive stereocilia) and thus to determine the relationship between the receptor potentials and displacement of their stereocilia. As a means of circumventing this technical difficulty, we have developed an organ culture of the mouse cochlea and here we describe the receptor potentials generated by the hair cells in response to direct displacement of their stereocilia.     

Na-Ca exchange current in mammalian heart cells

Electrogenic Na-Ca exchange has been known to act in the cardiac sarcolemma as a major mechanism for extruding Ca ions. Ionic flux measurements in cardiac vesicles have recently suggested that the exchange ratio is probably 3 Na:1 Ca, although a membrane current generated by such a process has not been isolated. Using the intracellular perfusion technique combined with the whole-cell voltage clamp, we were able to load Na+ inside and Ca2+ outside the single ventricular cells of the guinea pig and have succeeded in recording an outward Na-Ca exchange current while blocking most other membrane currents. The current is voltage-dependent, blocked by La3+ and does not develop in the absence of intracellular free Ca2+. This report presents the first direct measurement of the cardiac Na-Ca exchange current, and should facilitate the study of Ca2+ fluxes during cardiac activity, together with various electrical changes attributable to the Na-Ca exchange and the testing of proposed models.