Intracellular chloride and the mechanism for its accumulation in rat lumbrical muscle.

Abstract

SUMMARY1. Double-barrelled Cl--sensitive microelectrodes have been used to measure the intracellular Cl-activity (a',) and membrane potential (Em) in rat lumbrical muscles. The mean Cl-equilibrium potential (Ecl), calculated from the measured aC1 in sixty fibres, was 29 + 25 mV (S.D. of an observation) less negative than Em. The value of a', was higher than would be expected for a passive distribution, by a mean 1P4 + 1 2 mm. The mean Em was -59-5 + 8-2 mV. 3. If lack of selectivity of the Cl--sensitive ion exchanger and the intracellular presence of interfering anions, assumed to be responsible for the apparent al1 recorded in Cl--depleted fibres, were also responsible for the apparently non-passive Cl-distribution recorded under normal conditions, the difference between the calculated EC1 and Em would increase at more negative potentials. This was not observed over a range of Em values between -46 and -84 mV. 4. Inhibition of the Cl-permeability by application of 9-anthracene carboxylic acid (9-AC) resulted in an immediate rise in ai1 and hyperpolarization. An ai1 up to 40 mm higher, or eleven times higher, than that predicted by a passive distribution was recorded. Application of 9-AC after depletion of intracellular Cl-in Cl--free solution had no effect on either the apparent ai1 or Em.5. It is concluded that Cl-ions are actively accumulated by the skeletal muscle fibre and that the Cl-distribution therefore normally exerts a depolarizing influence.6. In the presence of 9-AC and nominal absence of CO2 and HC03-, readdition of Cl-to Cl--depleted fibres resulted in a substantial rise in a', and a small, maintained 7. Neither application of CO2 and HCQ3-nor application of DIDS (4,4'-diisothiocyanostilbene-2,2'-disulphonic acid) had any effect on the accumulation of Cl-ions. This suggests that Cl--HC03-exchange is not involved.8. Removal of Na+ or K+ resulted in a limited rise in a'1 such that EC1 approximated to Em. Removal of both cations had no greater effect than the absence of only one. Readdition of the cations caused an immediate accumulation of Cl-ions and divergence of Ec1 from Em. This was largely inhibited by the presence of frusemide. These results suggest that a Na+, K+, Cl-co-transport mechanism is responsible for the inward transport of Cl-.

Rapid co‐transport of sodium and chloride ions in giant salivary gland cells of the leech Haementeria ghilianii.

“…This compares with the following mean values for Cl-accumulation in other studies: 0 1 mm min' in sheep Purkinje fibres (Vaughan-Jones, 1979); 1 mm min-in rat lumbrical muscle (Aickin, Betz & Harris, 1989); 2-4 mm min-in smooth muscle of guinea-pig vas deferens (Aickin & Brading, 1982); and 1P3 mm min-in frog dorsal root ganglion cells (AlvarezLeefmans et al 1988). In each case the experimental protocol was similar to the present, i.e.…”

Ca(2+)‐dependent heat production by rat skeletal muscle in hypertonic media depends on Na(+)‐Cl‐ co‐transport stimulation.

“…However, as already pointed out, this co-transport can only continue, during the hyperosmotic steady state, thanks to the sustained stimulation of active Na+-K+ transport due to the increase of intracellular Na+ ion concentration. Now it is evident that none of the usual criteria by which Na+-K+-Cl-co-transport is defined -86Rb+ uptake in presence and absence of bumetanide (Burnham, Kidd & Palfrey, 1990); dependency on extracellular K+ (Aickin, Betz & Harris, 1989); bumetanide binding site solubilization and purification studies (Turner & George, 1990) -allows one to unambiguously exclude that this three-ion system simply results from a combination of Na-Cl-co-transport and active Na+-K+ transport. In fact, some close functional association of Na+-Cl-co-transport, which is a secondary-active transport process, with the primary-active Na+-K+ transport system is even suggested by the finding, in two non-muscle cell types, that the Na+-K+-Cl-co-transport system is dependent upon intracellular ATP concentration (Homma, Burns & Harris, 1990;Flatman, 1991).…”

In skeletal muscle the relaxation of the resting membrane potential induced by K+ permeability changes depends on Cl? transport

“…The net result is a small Cl − accumulation [1,2], which can be inhibited by the diuretic bumetanide and activated by hypertonicity [18,19,27,33,34,41,42]. In practice, P Cl in muscle is variable with age [11], can be reduced by denervation [20], and is an index for myotonic and dystrophic conditions [9,11].…”