Cyclic GMP and outer hair cell electromotility

The aim of this study is to examine the effect of phosphorylation pathways on the electrically evoked fast motile response of isolated outer hair cells (OHCs). Transcellular electrical stimulation was applied in the microchamber to guinea pig OHCs and motility was measured before and after drug application. Forskolin (adenylate cyclase activator), phorbol 12- myristate 13-acetate (PMA, protein kinase C activator) and dibutyryl 3',5'- cyclic guanosine monophosphate (cGMP agonist) were studied. As controls, L15 medium and dimethyl-sulfoxide (DMSO) were used. In each group, 12 cells were measured. Forskolin and PMA were dissolved in 0.1% DMSO to render them membrane permeable. DMSO by itself caused a statistically significant electromotility magnitude decrease. Forskolin and PMA could not reverse the motility decrease due to DMSO, the effects seen in their presence were the same as observed with DMSO alone. Thus, neither 3',5'-cyclic AMP-dependent protein kinase nor calcium/phospholipid-dependent protein kinase appear to have modulatory effects on electromotility. Dibutyryl cGMP (DBcGMP), in concentrations of 200 μM, elicited a significant electromotility magnitude increase. The DBcGMP effect could be inhibited by co-application of 200 μM DBcGMP and 100 μM 8-Rp-pCPT-cGMPS (8-4-chlorophenylthio-guanosine 3',5'- cyclic monophosphothioate, Rp isomer, a cGMP antagonist). Our results suggest that OHC electromotility is modulated by a cGMP-dependent pathway.