Chloride fluxes in crab muscle fibres.

1. Isotopic techniques were used to study the efflux of Cl(-) from single cannulated muscle fibres of the crab Maia squinado.2. The efflux of (36)Cl(-) was found to be exponential with steady rate constants ranging from 0.01 to 0.07 min(-1). The steady efflux was ca. 1000-2000 pM cm(-2) sec(-1). The efflux was slightly depressed by K(+)-free saline and was unaffected by 40 mM-K(+) saline and NO(3) (-) saline. The influx and efflux of Cl(-) were presumed independent.3. The membrane conductance calculated from (36)Cl(-) flux data was consistent with that determined by the method of electrotonic spread for other marine crustacean muscle fibres. Cl(-) accounted for most of the membrane conductance.