Effects of Adenylate Cyclase Activation on Electrical Resistance of Scala Media

Electrical resistance of scala media at the second turn of the guinea pig cochlea was measured while cochlear adenylate cyclase was activated by perilymphatic perfusion with 2 x 10(-4) M forskolin. The electrical resistance decreased from the pre-forskolin value (6.36 +/- 0.27 k omega to 5.22 +/- 0.33 k omega, n = 5), while the endocochlear potential (EP) increased from the pre-forskolin value (70.2 +/- 2.1 mV to 81.2 +/- 2.8 mV, n = 5). The time course of the electrical resistance change was more rapid than that of the EP change but almost identical to the time course of the change in the Cl- activity of the endolymph. The results suggest that the forskolin-induced decrease in the electrical resistance of the perilymph-endolymph barrier (presumably Reissner's membrane), and the consequent increase in Cl- flux into the endolymph may trigger EP elevation.