Stretch-activated ion channels in guinea pig outer hair cells

Two types of stretch-activated (SA) ion channels have been found in the lateral wall of isolated outer hair cells (OHC) from the guinea pig cochlea. One type had a reversal potential of -12 mV and was non-selective to cations, passing Ca²⁺ as well as monovalent ions. The channel had a conductance of 38-50 pS and the amplitude of the current through the open SA channel was independent of suction. The probability of the channel being open increased with applied suction and was voltage dependent with the maximum probability occurring at pipette potentials of -40 to -60 mV. The second type of SA channel had a conductance of approximately 150 pS and a reversal potential of approximately -50 mV. The ionic selectivity of this channel has not yet been determined, but it is probably K⁺ selective. OHCs have been shown to undergo a slow change in length in response to acoustic stimulation directed at the lateral wall of the OHC. The SA channels reported here could affect the motile response by altering the membrane potential or by allowing the entry of free Ca²⁺ which could lead to a change in OHC length through the interaction of actin and myosin. SA channels could also play an important role in regulating the osmotic pressure of OHC thereby influencing its electro-mechanical response.