STRETCH-ACTIVATED NONSELECTIVE CATION, CL- AND K-CELLS OF REISSNERS MEMBRANE( CHANNELS IN APICAL MEMBRANE OF EPITHELIAL)

Ion channels on the apical membrane of epithelial cells (the surface f acing the endolymph) of acutely isolated Reissner's membrane from guin ea-pig cochlea were investigated by using patch-clamp technique in cel l-attached and inside-out configurations. Three types of ion channel w ere identified: namely, a stretch-activated nonselective cation, a chl oride and a potassium channel. When the pipette was filled with high-K + endolymph-like solution, the most significant channel activity was n onselective cation channels (85/110, 77% patches). The current versus voltage relationship was linear with a unitary conductance of 22.1 + 0 .4 pS and reversal potential (V-r) of 2.3 +/- 0.8 mV (n = 18). The cha nnel exhibited a lower conductance (14.0 +/- 0.6 pS, n = 8) to Ca2+. T he open probability was low (NPo congruent to 0.1) in cell-attached co nfiguration under +60 mV pipette potential and increased when the memb rane was stretched with negative pressure. The channel was blocked by 10 mu M extracellular Gd3+. The two other types of channels were a sma ll voltage-sensitive Cl- channel (6.0 +/- 0.3 pS; 91/99, 92% patches) and a K+ channel (congruent to 30 pS; 29/191, 15% patches). These chan nels might play roles in the regulation of cell volume, in balancing t he hydrostatic pressure across Reissner's membrane and in maintaining the electrochemical composition of endolymph.