A CATIONIC NONSELECTIVE STRETCH-ACTIVATED CHANNEL IN THE REISSNERS MEMBRANE OF THE GUINEA-PIG COCHLEA

The Reissner's membrane (RM) separates in the mammalian cochlea the K-rich endolymph from the Na+-rich perilymph. The patch-clamp technique was used to investigate the transport mechanisms in epithelial cells of RM freshly dissected from the guinea pig cochlea. This study shows a stretch-activated nonselective cationic channel (SA channel) with a linear current-voltage relationship (23 pS) highly selective for catio ns over anions [K+ approximate to Na+ (1) > Ba2+ (0.65) > Ca2+ (0.32) >> Cl- (0.14)] and activated by the intrapipette gradient pressure. Th e open probability-pressure relationship is best fitted by a Boltzmann distribution (half-maximal pressure = 37.8 mmHg, slope constant = 8.2 mmHg). SA channels exhibit a strong voltage dependency and are insens itive to internal Ca2+-ATP, and fenamates but are blocked by 1 mu M Gd Cl3 in the pipette. They are reversibly activated by in situ superfusi on of the cell with hyposmotic solutions. Kinetic studies show that de polarization and mechanical or osmotic stretch modify the closed and o pen time constants probably by a different mechanism. These channels c ould participate in pressure-induced modifications of ionic permeabili ty of the RM.