Effect of inhibitors and uncouplers on the Na pump of the Maia muscle fibre

1. A study has been made of sodium efflux from single muscle fibres of the crab Maia squinado, and of the effect of inhibitors and uncouplers on this efflux, using the microsyringe technique. 2. (i) Externally applied ethacrynic acid or injected ethacrynic acid produces 50% inhibition. The inhibitory state due to externally applied ethacrynic acid is shown to be sensitive to 40 mM-K+ in the bathing medium. (ii) Internally applied chlorpromazine causes 40% inhibition. (iii) Internally applied ethyl alcohol causes a slight increase or a slight decrease in Na efflux or no effect. (iv) Internally applied antimycin A produces a net inhibitory effect of almost 50%. (v) Internally applied rotenone produces a 60% inhibitory effect while fibres that fail to contract initially show about a 90% fall in efflux. (vi) The response pattern to internally applied oligomycin is similar to that of antimycin but the net inhibitory effect is only 25%. (vii) Internally applied atractylate produces 45% inhibition. (viii) Internally applied gramicidin A produces about 40% inhibition. (ix) Internally applied valinomycin is without an effect, but in the presence of 40 mM-K+ in the external medium there is marked inhibition of Na efflux. 3. The evidence put forward suggests that the Na pump of the Maia fibre is divided into two parts, one the Na+-K+-ATPase, driven by ATP and arginine phosphate (ArP), and the other, an electrogenic mechanism, driven by respiration and possibly direct coupling of glycolytic energy. The process of reverse electron flow can be invoked as a reasonable explanation of some of the observations made.