Chloride conductance across toad skin: Effects of ionic acclimations and cyclic AMP and relationship to mitochondria-rich cell density

The anionic conductance across toad (Bufo viridis) skin was studied using t he voltage-clamp technique following long-term (more than 10 days) acclimat ion to NaCl and KCl solutions. The non-specific baseline conductance was ap proximately 0.6 mScm(-2) and was similar in skins from all acclimation cond itions. The voltage-activated Cl- conductance (G(Cl)) was maximal in skins from distilled-water- and KCl-acclimated toads (>3 mS cm(-2)) and was great ly reduced following acclimation to NaCl solutions. Cyclic AMP (EC50 = 13 m u mol l(-1)) and isobutylmethyl xanthine (IBMX) (EC50 = 69 mu mol l(-1)) ex erted different effects on the activated conductance. IBMX only sensitized the activated conductance, whereas cyclic AMP (CPTcAMP) at high concentrati ons induced an increase in anionic conductance that was insensitive to elec trical potential. Furthermore, external Cl- was not required for the stimul atory effect of cyclic AMP, and the conductive pathway had low selectivity. The effects of the two agonists were reversible and depended on the acclim ation conditions. Following electrical measurements, the skin of the toads was removed and stained with silver to measure mitochondria-rich cell densi ty (D-mrc). There was no correlation between D-mrc and Cl- conductance in t he present study.