The resting potential of moth muscle fibre

Abstract

SUMMARY1. The membrane of the moth muscle fibre was tested for resting permeability to various ions: it is not permeable to Mg2+ or Ca2+; it is slightly permeable to Na+ and NH4+; it is appreciably permeable to Cl-, but C1-is passively distributed; it is apparently permeable to H+ but effects of HCO3-are not ruled out; and it is primarily permeable to K+.2. Measurement of the internal K+ activity showed that E. is less negative than the resting potential.3. In the presence of DNP, or under anoxia, the membrane potential approaches, EKE; there is a small concomitant decrease in effective membrane resistance.4. An increase in external Ca2+ concentration is accompanied by increased effective membrane resistance and an increase in amplitude of the negative resting potential.5. Cooling the membrane (below room temperature) decreased the amplitude of the resting potential by 4-16 mV per 10°C, and was accompanied by a large increase in effective membrane resistance.6. The experimental results most readily fit the hypothesis that the resting potential of the moth muscle fibre, although the membrane is highly permeable to K+, Cl-and apparently to H+, is primarily maintained by an electrogenic transport process which generates an ionic current across the membrane. The possibility that the concentration gradient of H+ ions is metabolically maintained at a level sufficient to explain the resting potential was considered to be unlikely but could not be directly excluded.

Proton permeability of the plasma membrane of rat cortical synaptosomes

“…A similar unusually high pH, sensitivity of Em (dEm/pH =20mV) was observed in moth muscle fibres and also ascribed to H + acting as a permeable cation [33]. In contrast, the increase of Em at high pH, in cultured rat hepatocytes derived from Ph4P+ distribution and electrophysiological measurements was attributed to electrogenic H + pumping [341.…”

Cold-induced depolarization of insect muscle: Differing roles of extracellular K+ during acute and chronic chilling

“…is generally regarded to be passively distributed in most insect muscles and therefore contribute little to V m (Djamgoz, 1987;Fitzgerald et al, 1996;Rheuben, 1972). If the remaining 20 mV of depolarization is driven by a change in V d , it may thus result from a cold-induced increase in P Na , or decrease in P K , which would drive membrane potential toward the muscle equilibrium potential for Na + (E Na =+28 mV; Fig.…”

The effects of carbon dioxide anesthesia and anoxia on rapid cold-hardening and chill coma recovery in Drosophila melanogaster

“…Although the mechanisms of chill coma onset are poorly understood, Goller and Esch (1990) suggest that it results from a loss of function of the ion channels necessary for maintaining the membrane potential, leading to voltage equilibration and a loss of muscle cell excitability. Since resting potentials in insects are mostly maintained by a Na + /K + ATPase (Huddart and Wood, 1966;Rheuben, 1972), Hosler et al (2000) suggest that its activity is temperature dependent, and coordination recovery after return to room temperature is dependent upon functional restoration of this pump. However, the underlying causes of chill coma recovery variation have not been investigated, it is unclear whether the mechanisms are shared with chill coma onset and the mechanisms permitting modification of chill coma recovery are almost certainly different to those involved in RCH or basal cold tolerance (Sinclair and Roberts, 2005).…”